Physics R#3 Flashcards
What is mass?
The amount of matter in an object.
What are the SI units of mass?
Kilograms (Kg) and grams (g).
What are the two main apparatus used to measure mass?
Beam balance and digital balance.
What is the function of a beam balance?
To compare masses.
What precaution should be taken when using a beam balance?
Place it on a horizontal (flat) surface.
What is another name for a digital balance?
Sensitive balance, top-pan balance, or electric balance.
What are two precautions when using a digital balance?
- Place it on a horizontal surface
- Check for zero error.
What is length?
The distance between two points.
What are the SI units of length?
Meters (m), kilometers (Km), centimeters (cm), and millimeters (mm).
What are three common apparatus used to measure length?
Meter ruler, measuring tape, micrometer.
What is a meter ruler used for?
To measure up to 1 meter.
What is a measuring tape used for?
To measure lengths greater than 1 meter.
What is a micrometer used for?
To measure very small lengths (less than 1 cm), such as the thickness of wire or paper.
How do you accurately measure the thickness of a sheet of paper?
- Check the zero reading of a micrometer.
- Measure the thickness of 20 sheets of paper.
- Divide the thickness recorded by 20.
- Repeat and take the average of results.
Extra:
* Use identical sheets of paper.
* Avoid parallax error by looking perpendicularly.
How do you measure the length of a non-curved object?
Use a ruler: End length – Starting length.
How do you measure the length of a curved object?
- Place the object between two wooden blocks or set squares.
- Use a ruler: End length – Starting length.
How do you measure the inner diameter of a ring?
Calculate the total length of the ring using a ruler.
Subtract the inner thickness of both sides of the ring.
What is time?
The measurement of the duration of an event.
What are the SI units of time?
Seconds (s), minutes (min), hours (h) (convert all to seconds).
What are two apparatus used to measure time?
Stopwatch and clock.
How do you measure the period of a pendulum?
- Use a pendulum and stopwatch.
- Check the zero reading of the stopwatch.
- Start the stopwatch when releasing the pendulum.
- Count 20 oscillations and record the time.
- Divide the total time by 20 to get the period of one oscillation.
- Repeat and take the average.
What are precautions in the pendulum experiment?
- Check for zero error.
- Don’t count too many oscillations to avoid loss of count.
What are two sources of error in the pendulum experiment?
- Human error: reaction time.
- Instrument error: zero error, battery empty.
What is volume?
The space occupied by matter.
What are the SI units of volume?
Cubic centimeters (cm³), cubic millimeters (mm³), cubic meters (m³).
How do you convert volume units?
The same as length but raised to the power of 3
cm³ to m³ (x 100^3)
What is the formula for the volume of a cube or cuboid?
L × W × H.
What is the formula for the volume of a cylinder?
πr²h.
What is the formula for the volume of a sphere?
4πr³/3.
How do you measure the volume of an irregular object?
Using the displacement method.
What apparatus are used in the displacement method?
Measuring cylinder, water, object, sinker (if needed).
Describe the steps of the displacement method.
- Add sufficient water to the measuring cylinder and record volume as V1.
- Submerge the object and record new volume as V2.
- Subtract V1 from V2 (V2 - V1) to get the volume of the object.
What are three precautions when using the displacement method?
- Avoid parallax error.
- Ensure the object is fully submerged.
- Use a sinker if the object is less dense than water.
What is density?
The mass per unit volume of a substance.
What is the formula for density?
Density = Mass / Volume (D = m/v).
What are the SI units of density?
Kilograms per cubic meter (Kg/m³) or grams per cubic centimeter (g/cm³).
How do you find the density of an object?
- Measure the mass using a digital balance.
- Measure the volume using the displacement method.
- Divide mass by volume (D = m/v).
What is the difference between accuracy and precision in measurements?
Accuracy refers to how close a measurement is to the true or accepted value, while precision describes the consistency or repeatability of multiple measurements.
How do significant figures and uncertainties affect the reporting of measurements?
significant figures reflect the digits in a measurement that are known reliably, and uncertainties indicate the possible error range; both are crucial for expressing the reliability and exactness of data.
What distinguishes systematic errors from random errors in experiments?
Systematic errors are consistent, repeatable mistakes (e.g., calibration issues) that skew all measurements in one direction, whereas random errors vary unpredictably and can be reduced by taking multiple measurements and averaging.
Why is regular instrument calibration important in experimental measurements?
Calibration ensures that instruments are providing accurate readings by correcting zero errors and other deviations, which is essential for maintaining measurement reliability.
What is a scalar quantity?
A quantity that only has magnitude (size).
Give five examples of scalar quantities.
Mass, time, distance, volume, density.
What is a vector quantity?
A quantity that has both magnitude and direction.
Give four examples of vector quantities.
Force, acceleration, velocity, displacement.
What is the difference between distance and displacement?
- Distance: The total path traveled between two points.
- Displacement: The shortest straight-line distance between two points.
What is the formula for average speed?
Averagespeed = Totaldistance / Totaltime
How can you find average speed from a distance-time graph?
Use the gradient:
(𝑦2− 𝑦1) / (𝑥2 − 𝑥1)
(riseoverrun)
What is maximum speed?
The highest speed recorded, found by identifying the steepest straight line on a graph.
What is instantaneous speed?
Speed at a specific moment in time.
How do you find instantaneous speed from a graph?
Draw a tangent to the curve and measure its gradient.
What is the formula for acceleration?
a = (v−u) / t
where:
* a = acceleration
* 𝑣 = final velocity
* 𝑢 = initial velocity
* 𝑡 = time
What is increasing acceleration? Give an example.
Acceleration that increases at an increasing rate.
* Example: 1𝑚/𝑠, 3𝑚/𝑠, 7𝑚/𝑠 (+2,+4)
What is decreasing acceleration? Give an example.
Acceleration that slows down over time.
- Example: 1𝑚/𝑠, 5 𝑚/𝑠, 7 𝑚/𝑠 (+4, +2)
- Occurs in cars reaching terminal velocity.
What is constant uniform acceleration? Give an example.
Acceleration that stays the same over time.
* Example: 1𝑚/𝑠, 3 𝑚/𝑠, 5 𝑚/𝑠 (+2, +2).
What is constant deceleration? Give an example.
Velocity decreases at a constant rate.
* Example: 10 𝑚/𝑠, 7 𝑚/𝑠, 4 𝑚/𝑠 (−3, −3)
What does a horizontal line on a speed-time graph mean?
Constant velocity (speed stays the same over time).
How do you calculate distance from a speed-time graph?
Find the area under the graph.
What formula do you use for a triangle’s area?
1/2 × Base × Height
What formula do you use for a rectangle’s area?
Length × Width
What formula do you use for a trapezium’s area?
1/2 × (Base 1+ Base 2) × Height
How do you estimate the area under a curved speed-time graph?
- Find the midpoint of the curve.
- Divide the area into two shapes.
- Approximate each area and sum them.
What is free-fall motion?
Motion under the effect of gravity only.
What is the acceleration due to gravity on Earth?
9.8𝑚/𝑠^2
(use 10𝑚/𝑠^2
in exams).
What happens to speed and acceleration in free fall?
- Speed increases as the object falls.
- Acceleration remains constant at 9.8 𝑚/𝑠^2
Does mass affect free fall?
No, all objects fall at the same rate when air resistance is ignored.
What does a straight, diagonal line on a distance-time graph mean?
Constant speed.
What does a horizontal line on a speed-time graph mean?
Constant velocity (no acceleration).
What does a curve on a distance-time graph mean?
Changing speed (acceleration or deceleration).
What does a downward-sloping speed-time graph mean?
Deceleration (slowing down).
What happens when an acceleration-time graph is a horizontal line above zero?
Constant acceleration.
What information can you extract from a velocity–time graph?
- The gradient (slope) of a velocity–time graph gives the acceleration
- The area under the curve represents the displacement of the object.
How do you determine instantaneous velocity using a graph?
Instantaneous velocity is found by drawing a tangent at the point of interest on a velocity–time graph; the gradient of this tangent line represents the instantaneous velocity.
What are the basic kinematic equations that are useful in motion analysis?
Common equations include:
* 𝑣 = 𝑢 + 𝑎𝑡
* 𝑠 = 𝑢𝑡 + (1/2)𝑎𝑡^2
* 𝑣^2 = 𝑢^2 + 2𝑎𝑠
where 𝑢 is initial velocity, 𝑣 is final velocity, 𝑎 is acceleration, 𝑠 is displacement, and 𝑡 is time.
Why is vector addition important when dealing with velocity and displacement?
Because velocity and displacement are vector quantities (having both magnitude and direction), using vector addition helps in accurately determining the overall effect when combining movements in different directions.
What is a force?
A force is any push or pull on an object. It is a vector quantity.
What is a resultant force?
The total force acting on an object in a certain direction.
How do you calculate resultant force when forces are in the same direction?
Add them and keep the same direction.
How do you calculate resultant force when forces are in opposite directions?
Subtract the smaller force from the larger one and keep the direction of the larger force.
How do you calculate resultant force when forces are perpendicular?
Use the Pythagorean theorem:
𝐹 = Sqrt(𝐹(1)^2 +𝐹(2)^2)
How do you find the resultant force when forces act at an angle?
- If they have the same starting point → Use the Parallelogram Method.
- If they follow each other → Use the Triangle Method.
What is gravity?
The force that pulls objects toward Earth.
What is the formula for weight?
w = m × g
where:
- 𝑤 = weight
- 𝑚 = mass (kg)
- 𝑔 = acceleration due to gravity (9.8 𝑚/𝑠², use 10 𝑚/𝑠² in exams).
What is friction?
A force that opposes motion between solid surfaces.
What is air resistance?
A force that opposes motion in air. It increases with speed or larger surface area.
What is upthrust?
An upward force that occurs in liquids and gases.
What is tension?
A force that acts in strings, wires, and cables (e.g., a ceiling fan hanging from a wire).
What is normal force?
A contact force exerted by a solid surface perpendicular to an object.
What is Newton’s First Law of Motion?
If the resultant force is 0, an object remains at rest or moves at constant velocity.
What is Newton’s Second Law of Motion?
The resultant force acting on an object is equal to mass × acceleration:
- 𝐹 = 𝑚 x 𝑎
What is the relationship between force, mass, and acceleration?
- Force (F) is directly proportional to mass (m).
- Force (F) is directly proportional to acceleration (a).
- Mass (m) is inversely proportional to acceleration (a).
What is Newton’s Third Law of Motion?
For every action, there is an equal and opposite reaction.
What happens immediately after a skydiver jumps?
He falls under the effect of his weight only → Acceleration is constant, speed increases.
What happens as the skydiver falls at the start?
His speed increases, so air resistance increases → Acceleration and resultant force decrease.
* Resultantforce = weight − airresistance
What happens when the skydiver reaches terminal velocity?
Air resistance = weight → Resultant force = 0 → Speed becomes constant. (Newton’s first Law)
What happens when the parachute opens?
Surface area increases, so air resistance > weight → The skydiver decelerates.
- Resultantforce = airresistance − weight
What happens when the skydiver reaches terminal velocity again?
His speed decreases, so air resistance decreases until it equals weight → He falls at a safe constant speed.
What is circular motion?
Motion where an object moves at constant speed but is always accelerating because its direction changes.
What is the force that keeps an object moving in a circle?
Centripetal force.
In which direction does centripetal force act?
Toward the center of the circular path.
What causes circular motion?
Friction between the object and the surface (e.g., car tires on a road).
What is a free‐body diagram and why is it useful in analysing forces?
A free‐body diagram is a simplified drawing that shows all the forces acting on an object. It helps visualize forces, resolve them into components, and set up equilibrium equations.
What is pressure in solids?
Pressure is the force that acts on an area.
What is the formula for pressure in solids?
𝑃 = 𝐹/𝐴
(Pressure = Force / Area).
What are the units of pressure in solids?
N/cm², N/m², or Pascals (Pa), where 1 Pa = 1 N/m².
What is pressure in liquids?
Pressure in liquids is the force exerted on the surrounding container.
What is the formula for pressure in liquids?
P = ρgh
(Pressure = Density × Gravity × Height).
What unit is used for liquid pressure?
Pascals (Pa), ensuring all values are in meters.
What is atmospheric pressure?
The pressure exerted by the air around us.
How do you calculate total pressure in a liquid?
Total Pressure = Atmospheric Pressure + Pressure due to Liquid.
What does it mean that fluid pressure is isotropic?
It means that pressure in a fluid is exerted equally in all directions—a principle known as Pascal’s Principle.
What is the difference between gauge pressure and absolute (total) pressure?
- Gauge pressure is measured relative to atmospheric pressure
- Absolute pressure is the total pressure including atmospheric pressure.
What is a moment?
The turning effect of a force about a pivot.
Formula:
* Moment = Force × Perpendicular Distance from Pivot
What happens if a force acts on the pivot?
The perpendicular distance d = 0, so the moment = 0.
What happens if the total moment clockwise is greater than the total moment anticlockwise?
The object will turn clockwise.
What happens if the total moment clockwise is less than the total moment anticlockwise?
The object will turn anticlockwise.
What happens if the total moment clockwise equals the total moment anticlockwise?
The object is balanced and in equilibrium.
What are the two conditions for an object to be in equilibrium?
No resultant force acts on the object:
* Force up = Force down
* Force right = Force left
No resultant moment acts on the object:
* Total Moment Clockwise = Total Moment Anticlockwise
What are the steps to solve a moment problem?
- Calculate the moment caused by all given forces.
- Determine which forces are clockwise and which are anticlockwise.
- Use Total Moment Clockwise = Total Moment Anticlockwise to solve for missing forces or distances.
How do you calculate the force acting on a pivot?
Use the rule Force up = Force down (since the force direction is downward).
What is the center of mass?
The point at which the weight of an object acts.
How can you find the center of mass practically?
Move the object over a pivot until it balances. That point is the center of mass.
How can you find the center of mass for regular shapes?
The center of mass is located at the center of the 2D or 3D shape.
How can you find the center of mass for irregular shapes?
- Hang the object from a pin at any point.
- Use a plumbline to draw a line of weight.
- Repeat from at least three different points.
- The point of intersection of the lines is the center of mass.
Where is the center of mass in irregular objects with uneven weight?
It is shifted towards the heavier parts.
What factors increase the stability of an object?
- Lower center of mass (closer to the ground).
- Larger base area.
- The line of weight must be within the base area of the object.
What is the SI unit for moment, and how is moment defined?
The SI unit for moment is the Newton-meter (N·m). Moment is defined as the force multiplied by the perpendicular distance from the pivot.
What is Hooke’s Law?
Extension is directly proportional to load.
What is L₁?
The original unstretched length of an object.
What is L₂?
The stretched length of an object when a load is added.
How do you calculate extension?
Extension = L₂ - L₁
What are the three key features of a graph that follows Hooke’s Law?
- Straight line
- Passes through the origin
- As force increases, extension increases
What is the formula for Hooke’s Law?
Force = K × Extension (F = KX)
What is K in Hooke’s Law?
The spring constant (stiffness of the spring).
How do you calculate the spring constant (K)?
K = F/X (Use any values from the straight part of the graph).
What is the limit of proportionality?
The maximum load where a spring still obeys Hooke’s Law.
What happens when the limit of proportionality is exceeded?
The graph bends towards the extension axis and the object no longer obeys Hooke’s Law.
Are extension/force and length/force graphs the same?
Yes, but when calculating, we must account for the difference between L₁ and L₂.
What is the elastic limit in Hooke’s Law, and why is it significant?
The elastic limit is the maximum load or extension a spring can sustain and still return to its original shape. Hooke’s Law applies only within this elastic (or proportional) region.
What are the units of the spring constant
𝑘 in Hooke’s Law?
The spring constant
𝑘 is measured in Newtons per meter (N/m).
What is the formula for work?
Work = Force × Distance
What are the units of work?
Joules (J) or Newton-meters (Nm)
What is the relationship between energy and work?
Energy is the capacity to do work; work and energy are equivalent.
What is Gravitational Potential Energy (GPE), and what is its formula?
GPE is the energy an object has due to its height. Formula: GPE = mgh
How can GPE be increased?
By increasing mass or height.
What is Kinetic Energy (KE), and what is its formula?
KE is the energy due to motion.
Formula: KE = ½ m v²
What are some other forms of energy?
- Elastic potential energy (due to change in shape)
- Chemical energy (stored in chemical compounds)
- Thermal/Heat energy (lost due to friction)
- Nuclear energy (from radioactive elements)
- Solar energy (from the Sun’s light)
- Electric energy (due to charges)
What is the law of conservation of energy?
Energy cannot be created nor destroyed, only transformed from one form to another
How can we calculate velocity when only given height?
v = √(2gh)
What happens to kinetic energy when an object hits the ground?
- If it stops immediately, all KE is lost as heat and sound.
- If it rebounds, some KE is lost as heat and sound.
How does air resistance affect energy?
Some energy is lost as heat and sound due to friction with air.
How is energy converted in a pendulum?
- At the highest points: All energy = GPE
- At the lowest points: Energy = KE + GPE
How does friction affect a moving bicycle?
Some energy is lost as heat due to friction, reducing the KE at the lowest point.
What is power, and what is its formula?
Power is the rate of doing work.
* Power = Work / Time
* Power = Energy / Time
* Power = Force × Velocity
What are the units of power?
Watts (W) or Joules per second (J/s)
What is efficiency, and how is it calculated?
Efficiency is the ratio of useful output energy to input energy.
* Efficiency = (Useful Output Work / Input Energy) × 100%
* Efficiency = (Useful Output Power / Input Power) × 100%
How can we improve efficiency?
- Increase useful output energy
- Reduce wasted energy
- Use less input for the same result
What are common examples of fossil fuels?
Coal, natural gas, oil, and petrol.
What is one advantage of using fossil fuels for electricity?
They provide a high output of energy and can generate electricity continuously.
What are two disadvantages of fossil fuels?
They are non-renewable and cause pollution (including acid rain and global warming).
How do nuclear fuels generate electricity?
Through nuclear fission, which produces heat to create steam that drives a turbine connected to a generator.
Name two advantages of nuclear power.
It offers a very high output of energy and continuous generation of electricity.
Name one disadvantage of nuclear power.
It requires strict safety measures and produces dangerous nuclear waste.
Which energy sources typically use thermal power stations?
Fossil fuels and nuclear fuels.
How do thermal power stations produce electricity?
They burn fuel or use nuclear reactions to boil water, producing steam that turns a turbine connected to a generator.
How is geothermal energy converted to electricity?
Water is heated by hot rocks deep underground, creating steam that drives a turbine and generator.
Give two advantages of geothermal energy.
It is renewable and has no direct fuel costs.
Give two disadvantages of geothermal energy.
Limited suitable locations and the high cost/difficulty of deep drilling.
How do hydroelectric and tidal power stations generate electricity?
They use the potential energy of water (falling or tidal) to drive turbines connected to generators.
What is one advantage of hydroelectric or tidal power?
They are renewable and have no fuel costs.
What is one disadvantage of hydroelectric or tidal power?
They can be expensive to build and may cause environmental damage.
How is wind energy converted into electricity?
The kinetic energy of moving air turns turbine blades, which drive a generator.
Name one advantage of wind energy.
It is clean, renewable, and has no fuel cost.
Name one disadvantage of wind energy.
It provides relatively low output and requires a large, consistently windy area.
How do solar panels generate electricity?
They convert sunlight (light energy) directly into electrical energy.
What is one advantage of solar energy?
It is renewable, clean, and requires no fuel cost.
What is one disadvantage of solar energy?
It depends on weather/sunlight availability and can be expensive
How can wave energy be used to produce electricity?
The kinetic energy of ocean waves can drive turbines connected to generators.
Why is wave energy not widely used?
It’s often less efficient, location-specific, and can be technologically challenging or expensive.
How does biomass generate electricity?
The chemical energy in organic materials (like wood or waste) is released by burning, producing steam to drive a turbine and generator.
What is the difference between renewable and non-renewable energy sources?
Renewable sources do not run out (or can be used repeatedly), while non-renewable sources are finite and eventually deplete.
Which power station does not use any moving parts to generate electricity?
Solar panels
Name three energy sources that do not originate from the Sun.
Nuclear fission, geothermal, and tidal.
What is linear momentum, and what is its formula?
Momentum is mass × velocity. Formula: P = m × v
What are the units of momentum?
kg·m/s
How do we calculate the change in momentum?
- If momentum is in the same direction: ΔP = mv - mu
- If momentum is in opposite directions: ΔP = mv + mu
How is force related to change in momentum?
F = ΔP / t or F = m (v - u) / t
What is impulse?
Impulse is equal to change in momentum (ΔP) or Force × Time of contact
What does the law of conservation of momentum state?
Total momentum before a collision = Total momentum after a collision
What are the types of collisions?
- Elastic collision: KE is conserved (m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂)
- Perfect inelastic collision: Objects stick together; KE is lost (m₁u₁ + m₂u₂ = v(m₁ + m₂))
How does conservation of momentum apply to rockets?
Before launch, momentum is zero. When fuel burns, it produces downward momentum equal to the rocket’s upward momentum, making the rocket lift off.
How does conservation of momentum apply to a rifle and bullet?
When a bullet is fired forward, the rifle recoils backward with equal but opposite momentum.
How is efficiency defined in energy systems?
Efficiency is the ratio of useful output energy (or work) to the input energy, expressed as a percentage:
* Efficiency = (Usefuloutputenergy / Inputenergy)×100%
What is the relationship between impulse and momentum?
Impulse, defined as force multiplied by the time of contact (Impulse = F × t), equals the change in momentum of an object (ΔP). Momentum is a vector quantity given by mass times velocity.
What are the three states of matter?
Solid, Liquid, Gas
How are molecules arranged in solids, liquids, and gases?
- Solids: Regular arrangement, closely packed
- Liquids: Irregular arrangement, close together
- Gases: Irregular arrangement, far apart
How does intermolecular distance change across states of matter?
- Solids: Molecules are closely packed
- Liquids: Molecules are close together
- Gases: Molecules are far apart
How does intermolecular force compare in different states?
- Solids: Very strong
- Liquids: Strong
- Gases: Very weak
Which states of matter are compressible?
Only gases are compressible; solids and liquids are incompressible.
How does motion differ between solids, liquids, and gases?
- Solids: Vibrate in fixed positions
- Liquids: Pass by each other
- Gases: Move randomly and freely
Why are solids and liquids incompressible while gases are compressible?
- Solids: Molecules are tightly packed with strong forces.
- Liquids: Molecules are close together with strong forces.
- Gases: Molecules are far apart with weak forces, allowing compression.
What is Brownian motion?
The random movement of particles suspended in a fluid due to collisions with fast-moving molecules in the fluid.
What happens to a dust particle in air?
It moves freely and randomly in a zigzag path and is seen as a speck of light.
Why does Brownian motion occur?
Fast-moving air molecules hit the dust particle from all directions, causing random motion.
How does expansion compare in solids, liquids, and gases?
Expansion in solids < Expansion in liquids < Expansion in gases.
Why do gases expand more than solids?
Gas molecules are far apart with weak forces, allowing more expansion when heated.
What happens to a bimetallic strip when heated?
It bends towards the metal with lower expansion.
Give two disadvantages of expansion.
- Expansion in train railways
- Expansion in electric cables
What is Boyle’s Law?
At constant temperature, pressure is inversely proportional to volume
P₁V₁ = P₂V₂
What happens to gas pressure when volume decreases?
Pressure increases because molecules collide more frequently with container walls exerting more force and pressure.
What is the relationship between pressure and temperature at constant volume?
Pressure is directly proportional to temperature.
What happens to gas molecules when temperature increases?
They gain kinetic energy, move faster, and collide more frequently, exerting more force and pressure.
What is the relationship between volume and temperature at constant pressure?
Volume is directly proportional to temperature.
How do air molecules exert pressure on container walls?
Randomly and freely moving air molecules collide with the walls of the cylinder and rebound causing a change in momentum, which exerts force and pressure
What is the formula for heat energy?
Q = mcΔT
where:
* Q = Energy (Joules)
* m = Mass (kg or g)
* c = Specific heat capacity (J/kg°C | J/g°C)
* ΔT = Temperature change (°C)
What is thermal capacity?
The amount of energy needed to raise the temperature of a body by 1°C.
What is specific heat capacity?
The amount of energy required to raise the temperature of 1 kg/g of a substance by 1°C.
Why do materials with high thermal capacity take longer to heat or cool?
They require more energy to change temperature.
What happens to kinetic and potential energy during a temperature change?
- Kinetic energy increases
- Potential energy remains constant
What happens to kinetic and potential energy during a change in state?
- Kinetic energy remains constant
- Potential energy increases (for melting/boiling) or decreases (for condensation/freezing)
Why does evaporation cause cooling?
The most energetic surface molecules absorb energy from remaining liquid, leaving the remaining liquid with less energy and temperature
How can you increase the rate of evaporation?
- Increase temperature
- Increase air flow
- Increase surface area
- Decrease humidity
- Decrease liquid depth
How does conduction transfer heat (in metals)?
Thermal energy is transferred through metals by conduction. This is due to collisions between vibrating atoms and free electrons through atoms going from the hot to cold part
What materials are good conductors?
Metals (e.g., copper, aluminum) because they have many free electrons.
How can conduction be reduced?
Using insulators like plastic, wood, and rubber.
Where does convection occur?
In liquids and gases.
Why does hot air rise?
It has lower density and is replaced by cooler, denser air.
What is a sea breeze?
Cool air from the sea replaces warm air rising from land.
What is a land breeze?
Cool air from land replaces warm air rising from the sea.
How can heat loss by convection be reduced?
- Using a vacuum
- Using insulators
- Trapping air between layers
- Using a lid
How does radiation transfer heat?
Through electromagnetic (infrared) waves, even in a vacuum.
What are good absorbers of radiation?
Dark, dull, rough, black surfaces.
What are good reflectors of radiation?
Shiny, polished, white, and silver surfaces.
What is the greenhouse effect?
Greenhouse gases trap infrared radiation, increasing Earth’s temperature.
How can Earth’s temperature remain stable?
Incoming radiation from space = Outgoing radiation from Earth.
How does a car radiator lose heat?
- Heat transfers from engine to fluid by conduction.
- Heat transfers from fluid to radiator by conduction.
- The radiator is black with a large surface area to increase radiation emission.
How does a vacuum flask prevent heat loss?
- Double walls with vacuum: Reduces conduction & convection.
- Silvered walls: Reduces radiation loss.
- Lid: Reduces heat loss by convection.
What is the difference between specific heat capacity and thermal capacity?
- Specific heat capacity is the energy required to raise the temperature of 1 kg (or 1 g) of a substance by 1°C,
- Thermal capacity is the total energy needed to raise the temperature of an object by 1°C (specific heat capacity multiplied by its mass).
What are the three primary modes of heat transfer, and what is a key characteristic of each?
- Conduction: Energy transfer via direct collisions between particles (depends on thermal conductivity).
- Convection: Energy transfer through the bulk movement of fluids (driven by density differences).
- Radiation: Energy transfer via electromagnetic waves (does not require a medium).
How do pressure, volume, and temperature relate in an ideal gas (for constant T, V, or P)?
- At constant temperature (Boyle’s Law): 𝑃 ∝ 1/𝑉
- At constant volume: 𝑃 ∝ 𝑇
- At constant pressure: 𝑉 ∝ 𝑇
Why does the temperature remain constant during a phase change even though energy is transferred?
During a phase change, the energy is used to break or form intermolecular bonds rather than increasing the kinetic energy of the particles, so the temperature remains constant until the phase change is complete.
What is a wave, and what are its types?
A wave is a disturbance that transfers energy through a medium.
* Mechanical waves: Need a medium, cannot travel through a vacuum (e.g., sound waves, water waves, P-waves).
* Electromagnetic waves: Do not need a medium, can travel through a vacuum (e.g., light waves, radio waves).
What are transverse waves, and how do they differ from longitudinal waves?
- Transverse waves: Particles vibrate perpendicular to wave propagation, consist of crests and troughs (e.g., all waves except sound and P-waves).
- Longitudinal waves: Particles vibrate parallel to wave propagation, consist of compressions and rarefactions (e.g., sound waves, P-waves).
What happens during compression and rarefaction in longitudinal waves?
- Compression: Particles move closer, pressure increases.
- Rarefaction: Particles move farther apart, pressure decreases.
What is amplitude, and what are its units?
- Amplitude (A) is the maximum displacement from the rest position.
- Measured in mm, cm, or m.
What is wavelength (λ), and how is it measured in different types of waves?
- Wavelength is the distance between two successive crests/troughs (transverse) or two successive compressions/rarefactions (longitudinal).
- Formula: λ = total distance / number of waves.
What is frequency (f), and how is it calculated?
- Frequency is the number of waves that pass in one second.
- Formula: f = number of waves / total time.
- Unit: Hertz (Hz).
- Depends on the source of the waves.
What is periodic time (T), and how is it related to frequency?
- The time required for one complete wave.
- Formula: T = 1 / f or T = total time / number of waves.
What is wave speed (V), and how is it calculated?
- The speed at which a wave travels.
- Formula: V = λf or V = λ / T.
What are the laws of reflection?
- Angle of incidence = Angle of reflection.
- Angle of incidence: Between the incident ray and the normal.
- Angle of reflection: Between the reflected ray and the normal.
What is refraction, and how does a wave behave when moving between different mediums?
Refraction is the change in direction of a wave due to a change in speed and wavelength when moving between mediums.
* Deep to shallow / rarer to denser: Bends toward the normal, speed and wavelength decrease, frequency remains constant.
* Shallow to deep / denser to rarer: Bends away from the normal, speed and wavelength increase, frequency remains constant.
What is a wavefront, and what are its types?
- A wavefront is a surface where all points have the same wave properties.
- Types: Plane or spherical.
What are the properties of sound waves?
- Mechanical and longitudinal waves.
- Need a medium to transfer (cannot travel through a vacuum).
- Consist of compressions and rarefactions.
How does the speed of sound vary in different states of matter?
Solids > Liquids > Gases
* Gases: 100-900 m/s | Air: 320-340 m/s
* Liquids: 1000-2000 m/s | Water: 1500 m/s
* Solids: 2000+ m/s | Steel: 5000 m/s
How can the speed of sound be measured using the gun and smoke method?
- Fire a pistol and start the stopwatch when smoke is seen.
- Stop timing when the sound is heard.
- Measure the distance, repeat for accuracy, and calculate speed using distance/time.
How can the speed of sound be measured using the echo method?
- Produce a sound and time the delay until it is heard again.
- Measure the distance to the reflecting surface.
- Calculate speed using (2 × distance) / time.
How can the accuracy of speed of sound experiments be improved?
- Use a larger distance between observers.
- Repeat and take an average.
How is loudness related to amplitude?
- Amplitude is proportional to loudness: larger amplitude → louder sound.
- Loud sounds have narrower compressions and wider rarefactions.
How is pitch related to frequency?
- Frequency is proportional to pitch: higher frequency → higher pitch.
- Higher pitch means more compressions and rarefactions in a given time.
What are the frequency ranges of sound waves?
- Infrasonic: f < 20 Hz.
- Audible for humans: 20 Hz to 20,000 Hz (20 kHz).
- Ultrasonic: f > 20,000 Hz.
When a wave passes from one medium to another, which property remains constant and why?
- The frequency remains constant because it is solely determined by the source
- Only the wave’s speed and wavelength change during refraction.
Under what condition does significant diffraction occur for a wave passing through a slit?
Diffraction is most pronounced when the slit width is significantly smaller to the wavelength of the wave, allowing the wave to spread out.
How does temperature affect the speed of sound in air?
The speed of sound in air increases with temperature because the air molecules move faster, leading to more rapid energy transfer.
What are the main properties of light?
- Light is an electromagnetic wave.
- It does not need a medium to transfer (it can travel through a vacuum).
- It is a transverse wave (energy transfer is perpendicular to wave direction).
- It transfers energy from one point to another.
- It can reflect, refract, and diffract.
- Its speed in air/vacuum is 3×10^8 m/s.
- It consists of 7 colors (ROYGBIV).*
What is monochromatic light, and how does it compare to polychromatic light (white light)?
- Monochromatic light has one frequency/wavelength.
- Polychromatic (white) light contains multiple frequencies (the full ROYGBIV spectrum).
State the law of reflection in a plane mirror and list the image properties.
Law of reflection: Angle of incidence = Angle of reflection.
Image properties in a plane mirror:
* Upright (erect).
* Same size as the object.
* Virtual image.
* Laterally inverted.
* Distance from object to mirror = distance from mirror to image.
What is the difference between a real image and a virtual image?
- Real image: Can be formed on a screen; formed by actual rays coming from the object.
- Virtual image: Cannot be formed on a screen; formed by rays that only appear to come from the object.
Define refraction and explain why it occurs.
- Refraction is the change in direction of a wave as it passes from one medium to another.
- It happens because the wave’s speed and wavelength change in the new medium, causing the direction to bend.
What is Snell’s law for refraction from air to a medium and from a medium to air?
- Air to medium: 𝑛 = sin(𝑖) / sin (𝑟)
- Medium to air: 𝑛 = sin(𝑟) / sin (𝑖)
Define the terms 𝑖, 𝑟, and 𝑛, and explain how to calculate 𝑛 in terms of speeds
- 𝑖 = angle of incidence.
- 𝑟 = angle of refraction.
- 𝑛 = refractive index, which is the ratio: speedoflightinair / speedoflightinmedium
- A medium with a higher 𝑛 has lower light speed.
- In formula form: 𝑛 = (3×10^8) / 𝑣
What happens when light passes from air (rarer) into a denser medium (Case 1)?
- 𝑛(1) < 𝑛(2) and 𝑣(1) > 𝑣(2) || (fast to slow).
- The ray bends towards the normal (𝑖 > 𝑟)
- Use 𝑛 = sin(𝑖) / sin(𝑟)
.
What happens when light passes from a denser medium into air (rarer) (Case 2)?
- 𝑛(1) > 𝑛(2) and 𝑣(1) < 𝑣(2) || (slow to fast).
- The ray bends away from the normal (𝑖 < 𝑟)
- Use 𝑛 = sin(𝑟) / sin(𝑖)
What is the critical angle (Case 3) and how is it defined?
- The critical angle 𝑐 is the angle of incidence in a denser medium that produces a 90° angle of refraction in air (𝑟 = 90∘).
- 𝑖 = 𝑐: means the refracted ray just grazes the surface.
- 𝑛 = 1 / sin(𝑐)
Explain total internal reflection (Case 4) and when it occurs.
- Total internal reflection (TIR) happens when 𝑖 > 𝑐 (angle of incidence is greater than the critical angle) and light travels from a denser medium to a rarer medium.
- All light is reflected inside; no refraction leaves the medium.
What occurs when a light ray passes normally (i = 0°) to a surface (Case 5)?
The ray travels straight through without bending because there is no angle of incidence.
How do a reflecting prism and a parallel glass plate affect light rays?
- Reflecting prism: Can use total internal reflection or angled reflection (e.g., in a periscope) to change the light path.
- Parallel glass plate: The angle of incidence on the first surface equals the emerging angle from the second surface, making the incident ray parallel to the emerging ray.
What is special about a semicircular glass plate in refraction experiments?
Any ray incident on the curved (semicircular) surface at its center enters normally (Case 5), so it passes straight through without deviation.
How do optical fibres use total internal reflection?
- Optical fibres have a high 𝑛 interior layer and lower 𝑛 exterior layer.
- Light entering at suitable angles reflects internally (TIR) along the fibre without escaping.
How are optical fibres used in medicine?
- They are used in endoscopes for medical imaging.
- A fibre is inserted into a blood vessel or body cavity to reach an organ.
- Light travels inside the fibre by TIR to illuminate the organ and returns the image by TIR to a screen.
How are optical fibres used in communication?
- They carry telephone, internet, and TV signals at high data rates with more security over longer distances.
- TIR ensures minimal signal loss.
What is dispersion of light, and what happens to white light in this process?
- Dispersion is the splitting of white (polychromatic) light into its 7-color spectrum (ROYGBIV).
- Different wavelengths refract by different amounts, causing the colors to separate.
Which color has the longest wavelength and highest speed in a medium, and what does that cause?
- Red has the longest wavelength and thus the highest speed in a medium.
- It refracts the least and emerges first in dispersion (ROYGBIV order).
What is a convex (converging) lens, and how do you construct its ray diagrams?
A convex lens bends light rays inward, focusing them.
Ray diagram steps:
1. A ray parallel to the principal axis refracts through the focus.
2. A ray through the center of the lens continues undeviated.
3. A ray through the focus refracts parallel to the principal axis.
What is near-sightedness (short sight), and how is it corrected?
- A near-sighted person can see near objects clearly but not far objects.
- The image forms in front of the retina.
- It is corrected with a diverging (concave) lens.
What is far-sightedness (long sight), and how is it corrected?
- A far-sighted person can see far objects clearly but not near objects.
- The image forms behind the retina.
- It is corrected with a converging (convex) lens.
List the common properties of all electromagnetic waves.
- They travel at the speed of light in vacuum (3×10^8 m/s).
- They can propagate through a vacuum (no medium required).
- They are transverse waves.
What is the order of the electromagnetic spectrum from longest to shortest wavelength?
Radio waves → Microwaves → Infrared (IR) → Visible light → Ultraviolet (UV) → X-rays → Gamma (γ) rays.
How are radio waves used, and why can they pass through walls easily?
- Radio waves are used in non-satellite communications (TV, radio) and Bluetooth.
- Their long wavelength and low frequency let them penetrate walls.
How are microwaves used, and what adverse effect can they have?
- Uses: Cooking (microwave ovens), satellite communications, mobile phones.
- Adverse effect: Heating effect on tissues.
What are the uses and adverse effects of infrared (IR)?
- Uses: Remote controls, security alarm systems, night vision cameras.
- Adverse effect: Can cause skin burns.
What are the uses and adverse effects of ultraviolet (UV) radiation?
- Uses: Sterilization of medical equipment, hot missile tracking, security marking, sterilization of water.
- Adverse effects: Skin cancer, blindness/damage to retina.
How are X-rays and gamma (γ) rays used, and what are their adverse effects?
- X-rays: Bone photography, airport security, detecting hidden weapons.
- Gamma rays: Security systems, special cameras, sterilization of food.
- Both: Can cause cancer, mutations, and kill cells.
What is the difference between analogue and digital signals, and why are digital signals advantageous?
- Analogue signals: Continuous variation, prone to noise.
- Digital signals: Two-step voltages (0 = low, 1 = high), can be regenerated accurately, reduce noise, allow higher data transfer rates, and can be converted from analogue.
What is diffraction, and when is it most significant?
- Diffraction is the spreading of waves when they pass through a gap or around an obstacle.
- It is most significant when the gap size is similar to the wavelength.
- Longer wavelengths (e.g., radio waves) diffract more than shorter ones (e.g., light).
What is white light composed of, and how does dispersion separate it?
- White light is a combination of all visible colours (ROYGBIV).
- Dispersion occurs because different wavelengths refract by different amounts when passing through a prism.
Describe how light behaves when it refracts from air into a denser medium.
When light passes from air to a denser medium, its speed decreases, the wavelength shortens, and it bends towards the normal, while its frequency remains constant.
Which type of lens is used for near-sightedness (myopia) and why?
A diverging (concave) lens is used to correct near-sightedness because it moves the image from in front of the retina onto it.
What is the standard method for drawing ray diagrams for lenses?
- Draw one ray parallel to the principal axis (which refracts through the focal point)
- Draw one ray through the centre (which is undeviated)
- Draw one ray through the focal point (which refracts parallel to the principal axis)
What are the advantages of digital signals over analogue signals in communication systems?
Digital signals are less prone to noise, can be regenerated without quality loss, and support higher data transfer rates, leading to more reliable long-distance communication.
What are the two types of electric charges?
Positive charge (+) and Negative charge (–)
What is the law of attraction and repulsion for charges?
Like charges repel, unlike charges attract.
How can an object be classified based on its charge?
- Positively charged: more (+) than (–)
- Negatively charged: more (–) than (+)
- Neutral: equal number of (+) and (–)
What are good conductors and why?
Metals, because they contain a large number of freely moving electrons allowing charge to pass.
What are insulators and why?
Rubber, wood, plastic, because they contain few freely moving electrons and don’t allow charge to pass.
How can an insulator be charged?
By rubbing, transferring electrons between the objects.
Why must the cloth be dry when charging an insulator by rubbing?
Water is a conductor and would prevent effective charge transfer.
How can a conductor be charged by induction?
By bringing a charged rod close, allowing electrons to move, then grounding and removing the charge source.
What is an electric field?
The region surrounding a charge where an electric force is exerted.
What do electric field lines represent?
The direction and strength of the electric field; they originate from positive charges and enter negative charges.
What does a battery do in a circuit?
Converts chemical energy into electrical energy.
What is the voltage of a single cell?
1.5V
What is the function of a bulb in a circuit?
Acts as an indicator for electric current.
What is the function of a switch?
Controls the flow of current, typically drawn in an open position.
What is an ammeter used for, and how is it connected?
Measures current (A) and must be connected in series.
How is electric current defined and calculated?
The amount of charge passing per second:
𝐼 = 𝑄 / 𝑡
What is conventional current direction?
From the positive terminal of the battery to the negative terminal.
What is the function of a voltmeter and how is it connected?
Measures voltage (V) and must be connected in parallel.
What is Ohm’s Law?
V = IR
How is resistance calculated?
R = V / I
What happens to total resistance in a series circuit?
It increases:
𝑅(𝑇) = 𝑅(1) + 𝑅(2) + 𝑅(3)
What are disadvantages of series circuits?
If one component fails, all fail; brightness of bulbs decreases.
How is total resistance calculated in a parallel circuit? (for two resistors)
𝑅(𝑇) = (𝑅[1] x 𝑅[2]) / (𝑅[1] + 𝑅[2])
multiply / add
What are advantages of parallel circuits?
If one component fails, others work; bulbs maintain same brightness.
How does wire length affect resistance?
Longer wires have higher resistance.
How does cross-sectional area affect resistance?
Greater area results in lower resistance.
How does temperature affect resistance in metals?
Higher temperature increases resistance due to more collisions between electrons and the lattice.
How does temperature affect resistance in semiconductors?
Higher temperature decreases resistance.
What is the formula for resistance of a wire?
R = (ρxL) / A
What analogy explains current, voltage, and resistance?
- Current: Delivery crew carrying sandwiches
- Voltage: Energy sandwiches from battery to components
- Resistance: Traffic affecting crew’s movement
What is a rheostat?
A variable resistor used to control current.
What is a thermistor and how does it work?
A temperature-dependent resistor; lower resistance at high temperatures.
What is an LDR (Light-Dependent Resistor)?
A resistor that decreases in resistance when exposed to light.
What is a diode and how does it function?
A semiconductor that allows current to pass in one direction.
What happens when a diode is forward-biased? (connected forward)
It has low resistance and allows current to pass.
What happens when a diode is reverse-biased? (connected in reverse)
It has high resistance and blocks current.
What is an LED (Light Emitting Diode)?
A diode that emits light when forward-biased.
What are the three wires in a European plug?
- Live wire (carries electricity) [Blue]
- Neutral wire (closes circuit) [Brown]
- Earth wire (prevents shocks) [Yellow/Green]
What is a circuit breaker and how does it work?
A safety device that shuts down power when excessive current generates a strong magnetic field.
How does a fuse protect a circuit?
It melts when excessive current passes, breaking the circuit.
What are fuse ratings?
The fuse must be slightly larger than the normal operating current.
What is double insulation?
The outer case of a device is made of an insulator to prevent electric shocks.
What is a potential divider?
A circuit that divides voltage based on resistor values.
What happens in a variable resistor with a sliding contact?
Moving the slider changes the length, resistance, and voltage.
What is the difference between direct and alternating current?
- DC (Direct Current): Flows in one direction (batteries).
- AC (Alternating Current): Changes direction periodically (generators).
How do you charge a conductor negatively by induction?
To charge negatively by induction, bring a positively charged rod near a neutral conductor so that electrons in the conductor are attracted toward the rod. While the rod is in place, connect the conductor to ground; electrons will flow from the ground into the conductor, giving it a net negative charge. Then remove the ground connection and finally remove the rod.
Why does the V–I graph of a filament lamp deviate from a straight line?
- As current flows through a filament, it heats up, causing its temperature to increase.
- As temperature increases lattice of material vibrates more and collides more with electrons, therefore current decreases and resistance increases.
- This rising resistance results in a non-linear (curved or plateauing) V–I graph rather than a straight line as predicted by Ohm’s law for constant resistance.
What factors determine the resistance of a wire, and what is the governing formula?
The resistance of a wire depends on its material’s resistivity (ρ), its length (l), and its cross-sectional area (A). The formula is:
* 𝑅 = (𝜌 × 𝑙) / 𝐴
How do electric field lines indicate both the direction and strength of an electric field?
Electric field lines start from positive charges and end on negative charges. Their direction shows the field’s direction, and the closer the lines are to each other, the stronger the field at that region.
How does a potential divider work in a series circuit?
In a potential divider, the voltage drop across each resistor is proportional to its resistance. By adjusting the resistor values (or moving a slider on a resistance wire), you obtain a desired fraction of the total voltage.
What are the proper ways to connect an ammeter and a voltmeter in a circuit?
An ammeter is connected in series to measure the current flowing through the circuit, whereas a voltmeter is connected in parallel across a component to measure the voltage drop.
What are the key differences between alternating current (AC) and direct current (DC)?
- DC flows in one constant direction (typical of batteries)
- AC periodically reverses direction and its magnitude varies with time (typical of generators)
How does a diode function in forward and reverse bias?
- In forward bias, a diode has low resistance and allows current to pass
- In reverse bias, it exhibits high resistance and blocks current flow.
- This property is used, for example, in converting AC to DC.
What is the law of attraction/repulsion for magnets?
Like poles repel; unlike poles attract.
What are the basic properties of a magnet?
Magnets have a north and a south pole (there are no monopole magnets), are made of iron or steel, and do not affect non-magnetic materials.
What are permanent (hard) magnets and what are they made of?
Permanent magnets are made of steel and keep their magnetism for a long time.
What are temporary (soft) magnets and what are they made of?
Temporary magnets are made of iron and lose their magnetism after a short time.
How can steel be magnetized by stroking?
By moving a magnet on a steel bar in one direction many times.
How can steel be magnetized using DC current?
By moving a steel bar inside a coil that is carrying a DC current.
What are the methods to demagnetize a magnet?
- By hammering repeatedly
- By heating until red hot
- By moving a magnet inside a coil carrying AC
What is a magnetic field?
It is the region surrounding a magnet where magnetic force acts.
How do magnetic field lines run around a magnet?
They come out of the north pole in all directions and go into the south pole from all directions.
How does the spacing of magnetic field lines relate to the field’s strength?
As the spacing between lines increases, the magnetic field strength decreases.
Where is the magnetic field strongest and weakest?
It is strongest near the poles and weakest near the center.
How can you find the strength of a magnetic field using iron filings?
Place the magnet on paper sprinkled with iron filings; the pattern shows the field strength.
How can you determine the direction of a magnetic field using needle compasses?
Place needle compasses at different positions around the magnet to observe the orientation of the needles.
How can the magnetic field produced by a current-carrying wire be increased?
- Increase the current/voltage
- Increase the length of the wire
- Move closer to the wire
How can the magnetic field from a coil be increased?
- Increase the current/voltage
- Increase the number of turns in the coil
- Use an iron core
Inside the coil the field lines are straight and parallel.
What are electromagnets and how do they operate?
- Electromagnets are magnets that can be switched on or off. When switch is closed, current passes through the coil and magnetizes an iron core (producing a strong field)
- When open, no current flows and no field occurs.
How can you increase the magnetic field of an electromagnet?
- Increase the current/voltage
- Increase the number of turns in the coil
- Use an iron core
What is a relay and how does it use magnetic fields?
- A relay uses a small current circuit to operate a circuit that uses a large current
- Closing the switch sends current through a coil, creating a magnetic field that attracts a free contact to close the circuit and power a motor.
What is the function of a circuit breaker in a magnetic field?
It uses the magnetic effect to reduce the current to its normal value when excess current flows through a wire in a magnetic field.
How can the magnetic force acting on a moving wire be increased?
- By increasing current/voltage
- By increasing the number of turns of the coil
- By using a stronger magnet
What causes a coil to rotate in a magnetic field?
Two equal and opposite forces (one acting downward on AB and one upward on CD) create a moment that rotates the coil.
How can you increase the speed of rotation of a coil?
- By increasing current/voltage
- By increasing the number of turns of the coil
- By using a stronger magnet
How can the direction of rotation of a coil be reversed?
- Reverse the current
- Reverse the poles of the magnet
What is the function of a DC motor?
A DC motor converts electric energy into kinetic energy.
What is the role of split ring commutators in a DC motor?
They reverse the direction of current every half cycle, ensuring that the coil rotates continuously in one direction.
What is the purpose of carbon brushes in a motor?
Carbon brushes connect the rotating coil with the battery.
How is an induced current generated?
When a wire moves inside a magnetic field, the rate at which magnetic lines are cut changes, inducing a current.
How can you increase the induced current (emf) in a wire?
- By increasing the length of the wire
- By increasing the strength of the magnets
- By moving the wire faster
What does Faraday’s law of induction state?
The induced emf is directly proportional to the rate at which magnetic field lines are cut by the wire.
What does Lenz’s rule state about the direction of induced current?
The induced current is opposite to the normal current.
Is the induced current produced by a moving wire AC or DC?
It is alternating current (AC).
How can the induced current (emf) in a coil be increased?
- By increasing the number of turns in the coil
- By increasing the strength of the magnets
- By rotating the coil faster
What is an AC generator and when is its maximum and minimum currents reached?
- An AC generator converts kinetic energy into electrical energy
- The current is zero when the coil is vertical and maximum when the coil is horizontal
What is mutual induction in electromagnetic induction?
It is the process by which a changing magnetic field in one circuit induces a current in a nearby circuit.
How does the movement of a magnet relative to a stationary coil affect induced current?
- When the magnet moves toward the coil, current is induced
- When it moves away, induced current occurs in the opposite direction
- If both move together at the same speed in same direction, no current is induced.
How does induced current occur when the coil moves relative to a stationary magnet?
- The coil moving toward the magnet induces a current, and moving away induces current in the opposite direction
- If both remain at rest, no induced current occurs.
How do transformers work?
By electromagnetic induction. When alternating current/voltage passes through primary coil it produces an alternating magnetic field. This magnetic field magnetises the iron core. The magnetic field transfers to the secondary coil using iron core. The rate of magnetic field lines cut changes by secondary coil so induced current/e.m.f. occur in secondary coil.
Why wouldn’t a transformer work using DC?
A transformer wouldn’t work using DC as rate of magnetic field lines cut wouldn’t change
What is the relationship between primary and secondary coils in a transformer?
- Power is constant: 𝐼(𝑃) x 𝑉(𝑃) = 𝐼(𝑆) x 𝑉(𝑆)
- In step-up transformers: 𝑁(𝑃) < 𝑁(𝑆) so 𝑉(𝑃) < 𝑉(𝑆) and 𝐼(𝑃) > 𝐼(𝑆)
- In step-down transformers: 𝑁(𝑃) > 𝑁(𝑆) so 𝑉(𝑃) > 𝑉(𝑆) and 𝐼(𝑃) < 𝐼(𝑆)
Why is high alternating voltage used in the national grid instead of high alternating current?
- To reduce current
- To reduce heating effect
- To reduce energy lost
- Use thinner wires
- Cheaper
- Less metal used
- Less insulating material used
What are the key methods to increase magnetic effects in various devices?
- Increase current/voltage
- Increase the number of turns in coils
- Use stronger or iron cores
- Adjust proximity or movement speed
- When needed, reverse current or magnetic poles
What does the Right‑Hand Rule for Magnetic Fields around a straight wire state, and how do you use it?
Extend your right thumb in the direction of the conventional current (from positive to negative). Your curled fingers then show the circular magnetic field lines around the wire. Use this rule to determine the field direction around any straight current‑carrying conductor.
How is the Right‑Hand Rule for Magnetic Fields in Coils (Solenoids) applied, and what does it reveal?
Curl the fingers of your right hand in the direction of the conventional current flowing through the coil loops. Your thumb will point in the direction of the magnetic field inside the coil, indicating the north pole of the electromagnet. Use this rule to determine the polarity and field direction inside coils or solenoids.
What is Fleming’s Left‑Hand Rule (Motor Rule), and when should you apply it?
Hold your left hand so that the thumb, forefinger, and middle finger are perpendicular. The index finger shows the direction of the magnetic field, the middle finger the direction of the current, and the thumb the direction of the force (motion) on the conductor. Use this rule to predict the force direction on a current‑carrying conductor in electric motors.
Describe Fleming’s Right‑Hand Rule (Generator Rule) and its use in determining induced current direction.
Extend your right hand so that your thumb points in the direction of the conductor’s motion relative to the magnetic field, your index finger points in the direction of the magnetic field, and your middle finger then indicates the direction of the induced current. Use this rule when a conductor moves within a magnetic field, as in generators, to find the direction of the induced current.
Describe the magnetic field inside a solenoid.
- The magnetic field inside a solenoid is strong, uniform, and consists of straight, parallel lines.
- It resembles the field of a bar magnet, with distinct north and south poles at the ends.
What was the set up for Rutherford’s gold foil experiment and what were the observations?
- A beam of α‑particles was directed at a thin gold foil.
- Most particles passed straight through, indicating that atoms are mostly empty space.
- A few were deflected at small angles (showing a concentrated positive charge) and a very few were deflected back, confirming a tiny, dense, positively charged nucleus.
What did Rutherford’s experiment reveal about the structure of the atom based on the deflection of α‑particles?
- Most α‑particles were undeflected, showing that the atom contains empty space
- A few were slightly deflected, indicating a positive charge that repels α‑particles
- A few were greatly deflected, proving that the atom contains a tiny, heavy particle—the nucleus.
How did Rutherford use his experimental conclusions to develop his atomic theory?
He proposed that an atom consists of a tiny, heavy, positively charged nucleus surrounded by electrons in a largely empty space.
What is the standard atomic notation and what does each part represent?
Atomic notation is (_Z^A)X, where A (the mass or nucleon number) is the total number of protons and neutrons, and Z (the atomic or proton number) is the number of protons (with electrons equal to protons in a neutral atom).
What are isotopes and how do the carbon isotopes C‑12, C‑14, and C‑15 illustrate this concept?
- Isotopes are elements with the same number of protons but different numbers of neutrons.
- For carbon, all isotopes have 6 protons, C‑12 has 6 neutrons, C‑14 has 8 neutrons, and C‑15 has 9 neutrons.
How do stable and unstable elements differ in terms of energy and nuclear radiation?
Stable elements have no excess energy, whereas unstable elements contain excess energy that is released as nuclear radiation.
What are the three types of nuclear radiations and their standard symbols?
The three types are:
1. Alpha particles: (2^4)α
2. Beta particles: (-1^0)β
3. Gamma rays: (_0^0)γ
Describe the structure and air penetration of alpha particles.
- Alpha particles consist of 2 protons and 2 neutrons (like a helium nucleus)
- They can penetrate only a few centimeters in air
- They can be stopped by a sheet of paper
What are the key properties of alpha particles regarding ionization, mass, charge, and deflection in electric and magnetic fields?
- They have the highest ionization
- They are heavy (4 amu)
- They carry a charge of +2e
- They deflect toward the negative plate in an electric field
- They deflect anticlockwise in a magnetic field (using Fleming’s left-hand rule).
What is the structure, penetration distance, and stopping material for beta particles?
- Beta particles are fast-moving electrons
- They can travel a few meters in air
- They are stopped by aluminium foil (>5mm)
Outline the ionization, mass, charge, and deflection properties of beta particles.
- Beta particles have intermediate ionization
- They are light (mass equal to an electron) They carry a charge of –1e
- Deflect toward the positive plate in an electric field
- Deflect clockwise in a magnetic field (using Fleming’s right-hand rule).
What are the characteristics of gamma rays regarding structure, penetration, and stopping material?
- Gamma rays are high-energy electromagnetic waves with high frequency and short wavelength
- They have no mass and no charge
- They have the lowest ionization
- They are nearly unstoppable in air
- They are significantly reduced by lead (>2cm)
Why are gamma rays not deflected by electric or magnetic fields?
Gamma rays are high‑energy electromagnetic waves that have no mass and no charge, so they remain undeflected in both electric and magnetic fields.
What does ionization mean in the context of atomic physics?
Ionization is the ability of radiation to make an atom lose an electron.
Write the general equation for alpha decay and give an example using uranium-236.
- The general alpha decay equation is (_Z^A)X → (_Z–2^(A–4))Y + (_2^4)α.
- For example: (_92^236)U → (_90^232)Kr + (_2^4)α
Write the general equation for beta decay and provide an example using uranium-236.
- The beta decay equation is (_Z^A)X → (Z+1^A)Y + (-1^0)β.
- For example: (_92^236)U → (93^236)Bl + (-1^0)β.
What is the equation for gamma decay and what does it indicate about the nucleus?
The gamma decay equation is (_Z^A)X → (_Z^A)X + (_0^0)γ, which indicates that the nucleus remains unchanged.
How do the atomic and mass numbers change in alpha, beta, and gamma decays?
- In alpha decay, the atomic number decreases by 2 and the mass number by 4
- In beta decay, the atomic number increases by 1 while the mass number remains unchanged
- In gamma decay, there is no change in either number
Define ‘activity’ and ‘half-life’ in radioactive decay.
- Activity is the number of decays per second
- Half-life (T₁/₂) is the time required for the activity to decrease to half its initial value OR the time for radioactive nuclei to decrease to half its initial value.
How is the half-life determined from a decay curve?
- First, take the maximum value (e.g., 600 counts) and divide it by 2 (giving 300).
- Draw a horizontal line at 300 counts until it meets the decay curve
- Then drop vertically to the time axis; that time is the half-life (e.g., 1.5 hours).
What is background radiation and what are its common sources?
Background radiation is the natural radiation present around us in absence of radioactive material. The main sources are:
* Outer space (Sun and stars)
* Radon gas (about 60% of BG radiation)
* Rocks
* Nuclear experiments
* Nuclear wastes
* Medical imaging
How is background radiation measured and what is its typical count rate?
It is measured using a GM (Geiger-Muller) counter and is usually around 10-30 counts, although it can vary significantly.
How is the total count rate measured using a GM (Geiger-Muller) counter calculated?
The total count rate equals the sum of the count rate from the radiation source and the background count rate.
Which rule is used to determine the deflection direction of positive particles like α‑particles in a magnetic field?
Fleming’s left-hand rule is used when a current or positive particle (such as an α‑particle or proton) moves in a magnetic field.
Which rule applies to negative particles like β‑particles when deflected in a magnetic field?
Fleming’s right-hand rule is used for induced current or β‑particles (electrons) moving in a magnetic field.
Why do α‑particles have a higher ionization effect compared to β‑particles?
- α‑particles are heavier
- They carry a higher charge
So, they interact more strongly with matter, resulting in greater ionization.
What safety measures can be taken to reduce exposure to ionizing radiation?
To lessen ionization risks:
* Reduce exposure time
* Work from a large distance
* Use a protective screen
What are some practical uses of the three types of nuclear radiations?
- Alpha particles are used in smoke detectors
- Gamma rays are used for sterilizing food and treating cancer
- Beta particles are used to measure the thickness of paper sheets.
Compare nuclear fission and fusion, including examples of reactions and methods to control a chain reaction.
Nuclear fission:
* Splits a large nucleus into smaller nuclei
* Releases energy
* Ex: (_0^1)n + (_92^235)U → (_56^141)Ba + (_36^92)Kr + 3(_0^1)n
* Its a chain reaction
Nuclear fusion:
* Combines two small nuclei at very high temperatures to form a larger nucleus
* Releases energy,
* Ex: (_1^2)H + (_1^3)H → (_2^4)He + (_0^1)n.
Contoling chain reactions:
* By moderators (to slow the reaction)
* By control rods (to absorb neutrons)
How does radiometric dating (carbon dating) utilize radioactive decay?
- Radiometric dating compares the measured activity of a radioactive isotope (e.g., Carbon‑14) in a sample with its expected decay rate.
- Using the known half-life, the age of the sample can be estimated.
Which conservation laws must be obeyed in radioactive decay processes?
Mass number: Total number of nucleons remains constant.
Atomic number: Total positive charge is conserved.
Charge: Overall electrical charge is conserved.
Energy: Energy (including the energy carried by radiation) is conserved.
What is the relationship between the Earth and the Sun, and how does the Moon relate to the Earth?
- The Earth is a planet travelling in a nearly circular orbit around the Sun.
- The Moon orbits the Earth as a satellite.
How does the Earth move, and what does this motion cause?
Motion of Earth:
* The Earth spins about its axis (the line passing through the north and south poles) and makes one complete rotation every 24 hours. This causes day and night.
* The Earth’s rotation on its axis causes the Sun to have an apparent daily journey from east to west.
Why do seasons occur on Earth?
Seasons (Summer, Autumn, Winter, Spring) happen due to two factors:
* The rotation of Earth about the Sun once in 365 days (1 Year).
* The tilt of the Earth’s axis by 23.5° to the plane of its path around the Sun.
How long does it take for the Earth to orbit the Sun, and in what shape is this orbit?
The Earth orbits the Sun in approximately 365 days, and this orbit is nearly circular.
How long does it take for light from the Sun to reach Earth?
Light from the Sun takes about 500 seconds (around 8 minutes 20 seconds) to reach Earth.
What happens to day length on specific dates in the Northern and Southern Hemispheres?
Length of Days:
* The longest day for the Northern Hemisphere and the shortest day for the Southern Hemisphere is 21 June. (The Sun is highest above the horizon.)
* The longest day for the Southern Hemisphere and the shortest day for the Northern Hemisphere is 21 December. (The Sun is lowest above the horizon.)
How does the Moon move relative to the Earth, and what other properties does the moon have?
Motion of the Moon:
* The Moon is a satellite of the Earth.
* It rotates around Earth once every month.
* It rotates about its axis every month and always has the same side facing the Earth, so we never see the dark side of the Moon.
Other properties:
* It does not have an atmosphere.
* It has a low gravitational field compared with Earth.
What are the phases of the Moon, and why do they occur?
Phases of the Moon:
- In the new Moon phase, the Moon is between the Sun and the Earth, and the side facing the Earth is unlit, so it is not visible from the Earth.
- A thin new crescent appears along one edge as it travels in its orbit.
- The size of the crescent increases until it reaches the first quarter phase. In the first quarter phase, half of the Moon can be seen.
- At full Moon, the Moon is on the opposite side of Earth from the Sun and appears as a complete circle.
- After that, it wanes through the last quarter phase until only the crescent can be seen again.
- The Moon appears to have a daily trip across the sky, rising from east to west.
How can we calculate the average orbital speed of the Moon, and what do the symbols in the formula mean?
Orbital Speed: The average orbital speed. 𝑣 of the Moon is calculated by:
𝑣 =
* circumference / timeofonerotation
* 2𝜋𝑟 / 𝑇
where:
* 𝑟 is the radius of the orbit,
* 𝑇 is the time taken by the Moon to make one complete rotation around the Earth.
What does the Solar System consist of?
The Solar System:
* It consists of one star (the Sun) and eight planets moving around it in elliptical orbits.
* It includes dwarf planets and asteroids which orbit the Sun.
* Moons that orbit many planets.
* It contains comets and natural satellites.
What are the four inner planets, and what are their characteristics?
The Four Inner Planets: Mercury, Venus, Earth, and Mars. They are:
* Small in size
* Solid
* Rocky
* Have high density
What are the four outer planets, and what are their characteristics?
The Four Outer Planets: Jupiter, Saturn, Uranus, and Neptune. They are:
- Larger in size
- Colder
- Consist mainly of gases
- Have low densities
What is a dwarf planet, and can you give an example?
Dwarf Planets: For example, Pluto. They:
- Orbit the Sun at an average distance greater than Neptune.
What are asteroids, what are their characteristics, where are they mainly found, and what is a famous example?
Asteroids:
- Pieces of rock of various sizes
- Mostly orbit the Sun between Mars and Jupiter (the asteroid belt)
- Have a density similar to the four inner planets
- If asteroids enter the Earth’s atmosphere, they will burn up and fall to Earth as meteors.
- Larger asteroids are classified as dwarf planets.
- Asteroids are classified as minor planets, which are defined as any object that orbits a star that does not have a large enough mass for gravitational attraction.
- Famous asteroid: Ceres
What are comets,what are their characteristics, what is a famous example, and how do they behave when near the Sun?
Comets:
* Consist of dust embedded in ice made from water and methane.
* Have a density similar to the four outer planets.
* They orbit the Sun in highly elliptical orbits. Their distance from the Sun varies significantly.
* When comets approach the Sun, the dust and gas are blown backwards by radiation from the Sun, and the comet shows a bright head and a long tail pointing away from the Sun.
* Famous comet: Halley’s Comet
How do planets, dwarf planets, and comets orbit the Sun, and is the Sun at the center?
- Planets, dwarf planets, and comets orbit the Sun in ellipses.
- The Sun is not at the center of the ellipse.
- For approximating the circular paths of planets, the point can be taken as the center of the ellipse.
How do we use the orbital speed formula for other planets in the Solar System?
The same formula 𝑣 = 2𝜋𝑟 / 𝑇 can be used for any planet (including the Earth) to calculate average orbital speed
Where:
* 𝑟 is the average orbital radius and
* 𝑇 is the orbital period
How much of the Solar System’s mass is in the Sun, and how does this affect gravitational fields?
More than 99% of the mass of the Solar System is concentrated in the Sun. Because of this, the Sun has a much stronger surface gravitational field than the planets, and its gravitational attraction keeps all the objects in orbit.
According to the theory of origin, how did the Sun form?
The Sun is thought to have formed when gravitational attraction pulled together swirling clouds of hydrogen and dust called nebulae in a region of space where their density was high.
How did the planets form after the Sun?
- The planets are created from discs of matter that remain from the nebula that formed the Sun.
- As this material rotated around the Sun, gravitational attraction between small particles caused them to join together and grow in size in an accretion process.
- The evidence for this accretion model of the formation of the Solar System is the approximate age of the Earth being the same as the age of the Moon and the Solar System.
- Also, all planets orbit the Sun in the same plane and rotate in the same direction.
Where did the heavier chemical elements in the Sun and inner planets come from?
They might have come from an exploding supernova.
During the lifetime of a star, atoms of hydrogen and other light elements are fused into atoms of heavier elements.
Why are the inner planets different from the outer planets?
- As the Sun grew, it became hotter.
- In the region of space where inner planets were forming, the temperature would be high for light elements to form heavier elements.
- The inner planets are built of materials with high melting temperatures, such as metals and silicates.
- Further away from the Sun, in cooler regions, light molecules could exist in a solid icy form. The outer planets could grow large enough to capture the light elements.
- The outer planets are large, gaseous, and cold; together their mass is about 99% of the mass orbiting the Sun.
- More than 99% of the mass of the Solar System is concentrated in the Sun.
What factors affect the gravitational field strength of a planet?
The gravitational field strength of a planet increases when:
1. The mass of the planet increases.
2. The distance between the planet and the object decreases (the attraction force is inversely proportional to the square of the distance).
How does a planet’s year, orbital speed, and surface temperature vary with distance from the Sun?
- The planet’s year (time to orbit the Sun) increases with increasing distance from the Sun.
- The orbital speed decreases with increasing distance from the Sun.
- The surface temperature of the planet decreases as distance from the Sun increases.
What force keeps planets in orbit, and how does distance affect orbital speed?
- For planets orbiting the Sun in near-circular paths, the force of gravity between the Sun and the planet provides the necessary centripetal force.
- The strength of the Sun’s gravitational field decreases as the distance between the Sun and the planet increases, so the centripetal force will decrease. This results in a lower orbital speed and longer orbital duration.
How does the speed of a comet change as it orbits the Sun in a large ellipse?
- For a comet with a large elliptical path, its speed increases as it approaches the Sun and decreases as it moves away from the Sun.
- As the comet approaches the Sun, its kinetic energy increases.
- When it moves away, some of the kinetic energy is converted into potential energy.
What is the Sun made of, and what type of star is it?
- The Sun is a medium-sized star which consists mainly of hydrogen and helium.
- The radiant energy it emits is mostly in the infrared, visible, and ultraviolet regions of the electromagnetic spectrum.
- This radiation is emitted from glowing hydrogen, which is heated by energy released in nuclear fusion within the Sun.
How do nuclear reactions power stars like our Sun?
Nuclear Reactions in Stars:
* Stable stars such as our Sun are hot and dense enough for nuclear fusion of hydrogen into helium to occur, releasing large amounts of energy.
* The Sun is powered by a nuclear fusion process in its core.
* Some of the energy generated in the core transfers to the surface of the star. These surface layers are cooler and less dense, but they are hot and contain hydrogen gas that glows and emits electromagnetic radiation into space.
Why do stars vary in size, mass, surface temperature, color, and brightness?
Stars vary in size, mass, surface temperature, color, and brightness. Color and brightness both depend on the surface temperature, which increases with the mass of the star. A white or blue star is hotter than a red or yellow star.
What is a light-year, and why is it used?
- Stars are seen at night and appear close, but the distance between stars is very great.
- A new unit is used to measure these distances, which is the light-year.
- A light-year is the distance traveled in space or vacuum by light in one year.
- 1 light-year = 9.5×10^12 km = 9.5×10^15 m.
How does a protostar form, and what happens as it gains mass?
- When interstellar clouds of dust and gas containing hydrogen collapse under the force of gravitational attraction, a protostar is formed.
- As the mass of the protostar increases, its core temperature increases. When the core becomes hot enough, nuclear fusion can start.
- If the young star has a large mass, it forms a blue or white star. If it has a smaller mass such as our Sun, it forms a red or yellow star.
What is a stable star, and how long does this stage last for a star like the Sun?
- In a stable star (as in the Sun), the very strong forces of gravity pulling inwards are balanced by the opposing forces trying to make it expand due to extremely high temperatures.
- When forces are balanced, the star is in a stable state (for 10,000 million years). During this time, most of the hydrogen in the core is converted into helium.
(Refer to the Star Life Cycle diagram for a visual overview.)
What happens when a star starts to run out of hydrogen?
- It becomes unstable due to less energy being produced by nuclear fusion in the core.
- The core collapses inward under its gravitational force of attraction.
- Potential energy is converted into kinetic energy that makes the core hotter. A fast burn of remaining hydrogen takes place, and a large expansion occurs.
- The expansion and cooling of the surface gases makes the star turn into a red giant (most stars) or red supergiant if the star is massive.
- As the temperature of the core increases again, fusion of helium into carbon occurs.
(Refer to the Star Life Cycle diagram for a visual overview.)
How do low-mass stars end their life cycle?
- When all the helium is used up, the core collapses and becomes a white dwarf at the center of a glowing shell of ionized gas known as a planetary nebula.
- The white dwarf cools into a cold black dwarf containing carbon.
(Refer to the Star Life Cycle diagram for a visual overview.)
How do high-mass stars evolve, and what leads to a supernova?
- Massive stars burn up hydrogen more quickly than low-mass stars, so their stable stage is shorter.
- The core collapses into a supergiant, and nuclear fusion of helium to carbon occurs.
- When all helium has been used up, the core collapses further due to gravitational forces, and its temperature increases and becomes hot enough for the nuclear fusion of carbon into oxygen, nitrogen, and finally iron to occur.
- Nuclear fusion stops, and the energy of the star is released in a supernova explosion.
- In the explosion, there is a large increase in the star’s brightness, and the temperature becomes high enough for fusion of nuclei into heavier elements than iron. These heavy elements are thrown into space as nebula and become ready to form new stars and planetary systems.
(Refer to the Star Life Cycle diagram for a visual overview.)
What remains after a supernova, and under what conditions do neutron stars and black holes form?
- The center of the supernova collapses to a very dense neutron star, which spins rapidly and acts as a pulsar, sending out pulses of radio waves.
- If the red giant is very massive, a black hole is formed. In a black hole, the matter is packed so densely (the mass of Earth would occupy the volume of 1 cm³) that nothing can escape from its gravity, not even light. Intense X-ray radiation may be emitted, which alerts us to its presence.
(Refer to the Star Life Cycle diagram for a visual overview.)
What is a galaxy, and which galaxy does our Solar System belong to?
- A galaxy is a large collection of stars; there are billions of stars in a galaxy.
- The Milky Way is a spiral galaxy to which our Solar System belongs.
- Galaxies can be seen on dark nights as a narrow band of light spreading across the sky.
- Galaxies vary in size and number of stars. They travel in groups. The nearest spiral galaxy in our local cluster is the Andromeda Galaxy.
How large is the Milky Way Galaxy in light-years?
The Milky Way has a diameter of about 100,000 light-years.
How do we know the Universe is expanding, and what is redshift?
- The Universe is made of millions of galaxies.
- When light emitted from stars in distant galaxies is shifted to the red end of the electromagnetic spectrum, it is called redshift (the wavelength of light increases).
- The greater the redshift, the farther away the galaxy is from us. This is explained by the Doppler effect.
- If the source of light approaches us, the waves are crowded into a smaller space, and their wavelength decreases (blueshift). If the source moves away, the wavelength increases (redshift).
- From the size of the redshift of starlight, the speed of recession of the galaxy can be calculated, providing evidence that the Universe is expanding.
What is the Big Bang Theory, and what does it propose?
- If the galaxies are receding from each other, it follows that in the past they were closer together. Therefore, the matter of the Universe was packed together in an extremely dense state.
- The Big Bang theory proposes that this happened from one place with a huge explosion (Big Bang).
- Scientists cannot predict what will happen in the future because the density of the Universe is difficult to calculate. This is partly because 80% of the Universe is made of invisible materials that do not emit radiation.
- The gravitational force between masses is used to determine the motion and evolution of planets, stars, and galaxies, and it controls the fate of the Universe.
What is the cosmic microwave background radiation (CMBR), and why is it important?
Microwave Background Radiation:
- The Big Bang produced radiation energy in the form of cosmic microwave background radiation (CMBR) of a specific frequency. It fills the whole Universe with the same intensity in all directions.
- The CMBR was produced shortly after the Universe was formed.
- Since the Universe is still expanding, this results in a redshift of the cosmic background radiation into the microwave region of the electromagnetic spectrum.
How do we estimate the age of the Universe using Hubble’s Law?
Age of the Universe:
- It is found that the speed of recession (𝑣) of a galaxy is directly proportional to its distance away (𝑑). This is called Hubble’s Law:
- 𝑣 = 𝐻0 × 𝑑
- 𝐻0 (Hubble’s Constant) is defined as the ratio of the speed at which the galaxy is moving away from Earth to its distance from Earth.
- Hubble’s constant represents the rate at which the Universe is expanding at present. Its value is found by measuring the speed of recession of large galaxies whose distances are known.
- Redshifts are used to find the speed of recession, and distance can be calculated from the brightness. The apparent brightness decreases as the inverse square of the distance from the supernova.
- The estimated value of 𝐻0 is 2.2×10^−18 per second.
- The age of the Universe is equal to:
- 1 / 𝐻0 =1 / 2.2×10^−18 = 4.5 × 10^17 s.
