Whole Course Flashcards
Describe how a cyclist can streamline themself
- Crouch over the handlebars
- Wear tight lycra clothing
- Specially shaped helmet
What is meant by capacitance?
Charge stored per unit volt
An astronaut has a mass of 50kg. What will happen to the astronauts weight on the Moon?
The weight will decrease as there is a lower gravitaional field strength on the Moon.
Explain how a fusion reactor could generate electrical energy.
- At high temperature and pressure small nuclei join together
- This releases huge amounts of heat energy (Nuclear to Heat)
- The heat energy is used to heat water to steam.
- The steam is used to turn a turbine. (Heat to Kinetic)
- The turbine is used to turn a generator. (Kinetic to Electrical)
What is the energy change in a battery?
Chemical to electrical
Which circuit component is represented by the following diagram?
MOSFET
What is an asteroid?
An asteroid is a small rocky and airless object that orbit the sun. They are too small to be planets.
What will absorb beta radiation?
A few millimetres of aluminium
How can you tell from this oscilloscope image that this is AC?
The trace shows a change in direction
What are the issues of pressure differential?
Pressure in space is so low it is almost zero. Space suits and pressurised space craft are required to protect astronauts otherwise they would lose conciousness and suffocate or their blood could boil.
What happens if light is shone onto a surface at an angle greater than the critical angle?
It is no longer refracted it is totally internally reflected.
What happens to a light ray as it travels from water into air?
It speeds up and changes direction away from the normal.
What does the path a projectile takes look like?
Curve
What is the difference between mass and weight?
Mass is a measure of the partcles that make an object up. Weight is a force caused by the gravitational field strength of a planet.
What is the rule for voltages in a parallel circuit?
The voltage across each branch is equal to the supply voltage.
Why is maintaining energy such a big issue in space exploration?
Energy is required to maintain life support systems. It would be difficult to carry enough fuel so energy must be generated in space.
Name one source of AC
Mains supply
What is speed?
Distance travelled per second.
How should a diode or LED be connected with a battery to light correctly?
Small line on battery points to small line on LED or diode.
What is conservation of energy?
Energy cannot be created or destroyed it can only be transferred from one type to another.
What is the charge on an electron?
Negative
State one source of visible light.
- The Sun
- Light bulbs
- Anything hot enough to glow
What would the field lines around a positive point charge look like?
Field lines show direction away from the positive point charge.
Which component does the symbol represent?
Buzzer
What will be the voltage across a capacitor when it is fully discharged?
Zero volts.
What is a fuse?
Safety device that protects the flex
What is the difference in the diffraction pattern in a long wavelength and a short wavelength passing an object?
The longer wavelength diffracts more.
What is the symbol for an ammeter?
Circle with an A in it.
State one detector of gamma radiation
- Photographic film
- GM Tube
- Bubble chamber
Which circuit component is represented by the following diagram?
Transistor
What is the ‘observable universe’?
The observable universe is the furthest point that we can ‘see’ or detect.
What is a galaxy?
A galaxy is a gravitationally bound system of stars, stellar remnants, gas, dust and dark matter.
What is meant by the half-life of a source?
It is the length of time it takes for the activity of a source to drop to half of it’s original value.
What is the radiation known as alpha particles?
It is a helium nucleus.
(It has 2 protons and 2 neutrons.)
How can you identify a series circuit?
It is a circuit with only one path round it.
What is the energy chage in a battery?
Chemical to electrical
What are the three effects a force can have?
- Change the speed of the object
- Change the direction of travel of the object
- Change the shape of the object
State one use for gamma radiation.
- Used as a tracer in medicine
- Used to treat cancer
- Sterilisation of operating instruments
- In industry, radioactive “tracer” substances can be put into pipes and machinery, then we can detect where the substances go.
- Gamma rays kill microbes, and are used to so that it will keep fresh for longer. This is known as “irradiated” food.
- Checking for cracks in aeroplane wings and joints
If an object is projected horizontally or dropped, how can the vertical velocity just before it hits the ground be calculated?
Use a=(v-u)/t
u is 0ms-1
a is 9.8ms-2
v you are calculating
t is the time it falls for
a = (v-0)/t
v = at
An astronaut has a mass of 50kg. What will happen to the astronauts mass on the Moon?
It stays at 50kg. Mass does not change.
What is meant by equivalent dose rate?
Equivalent dose absorbed per unit time.
What is meant by the Big Bang?
It suggests that all the matter in the universe was in an infinitely small, hot and dense state which then expanded.
Will long or short wavelengths diffract more?
Lomg wavelengths diffract more.
How is a uniform electric field represented?
Evenly spaced field lines
What is a moon?
A natural satellite
Why is an LED normally connected in series with a resistor?
Resistor is to protect the LED by limiting the current in the LED.
What is a thermistor?
A resistor whose resistance changes with changes in temperature
Which circuit component is represented by the following diagram?
Loudspeaker
What is work?
It is the measure of the energy used to move an object over a distance using a force.
What is the link between the radiation weighting factor and the ionisation caused by a source?
The more ionisation the higher the radiation weighting factor.
State two place a variable resistor can be used.
Light dimmer switch sped control on Scalextric cars volume control on a radio
Which circuit component is represented by the following diagram?
Resistor
What happens if you increase the resistance in a circuit?
The current will decrease
What type of wave is a sound wave?
Longitudinal.
What is the symbol for an Ohmmeter?
Circle with an Omega in it
Name one source of AC
Mains supply
What is the charge on a gamma ray?
No charge
Why is travelling large distance in space such an issue?
Carrying the fuel required would be impossible.
What is the radiation known as gamma radiation?
It is a wave and part of the electromagnetic spectrum.
Explain how to measure the acceleration of the car using the equipment shown below and a stop watch.
- Car starts from rest so u = 0ms-1.
- When the car is released start the stop watch when it reaches the light gate stop the stop watch.
- This is t, the time for the change in velocity.
- When the cardboard passes through the light gate the timer attached to it records this time.
- Measure the length of the card with a ruler.
- The final velocity, v = length of card / time on timer
- Then calculate acceleration, a = (v-u)/t
What is the charge on a proton?
Positive
Should the engine force or the resultant force be used when calculating the acceleration of a space rocket on take off?
Resultant force
Name three vector quantities
- Displacement
- Velocity
- Acceleration
- Force
- Momentum
- Weight
What is meant by gravitational field strength?
Force per unit mass
Which line on the graph represents the corrected count rate? Give a reason for your answer.
It is the dotted red line.
You know this is the corrected reading as it is lower than the other reading as background has been subtracted.
This graph gives a 0 reading for the count rate, this is not possible as there is always background radiation so must be the corrected graph.
Which circuit component is represented by the following diagram?
Thermistor
What is the radiation weighting factor?
A number that takes into account the type of radiation you are exposed to.
How should a voltmeter be connected to measure the voltage across a component?
It should be connected across the component
What is meant by the potential difference (voltage) of a supply?
It is the number of Joules of energy given to each coulomb of charge passing through the cell
What is the energy change in a lamp?
Electrical to light (+ heat)
How does a relay work?
- Close a switch to make a current flow in a wire.
- This creates an electromagnet.
- Electromagnet attracts metal switch.
- This completes the second circuit and the lamp switches on.
What happens to the object at point X?
It changes direction
What is the weight of an object in freefall?
0 Newtons
What effect is shown here?
Diffraction
Which circuit component is represented by the following diagram?
Diode
What is latent heat of vaporisation?
The number of Joules of energy required to change 1kg of a liquid to 1kg of a gas with no temperature change.
Name a longitudinal wave.
Sound.
State one use for X-rays.
- Create images of bones to detect breaks
- Create images of organs for diagnosis
- Security to scan luggage at airports
- Doctors can give patients a “Barium Meal”, which is a drink of Barium Sulphate. This will absorb X-rays, and so the patient’s intestines will show up clearly on a X-Ray image.
What type of current is represented by this oscilloscope image?
AC
A temperature - time graph is shown below. What is happening at point E on the graph?
The temperature of the gas is increasing.
Explain how to use the equipment below to calculate the instantaneous speed of the car.
- Measure the length of the cardboard using a ruler.
- Roll car down the slope.
- When the cardboard breaks the beam it starts the timer connected to the light gate. When the cardboard has passed through the beam is remade and the timer stops.
- Speed = length of cardboard / time on timer
What would the field lines look between parallel plates?
Field lines run from positive to negative plate, with a bulge at the ends of the parallel plate.
How can you indicate a stronger electric field?
More field lines
What will absorb alpha radiation?
A few centimetres of air or a sheet of paper.
Which circuit component is represented by the following diagram?
Loudspeaker
Explain why the angle of re-entry poses a challenge.
The angle of re-entry to the atmosphere is important
- too steep and the change in kinetic energy being transferred to heat is too fast resulting in overheating and possible rocket break-up
- If the angle is too shallow you will skip off the atmosphere.
What is power?
The energy used per second
Which circuit component is represented by the following diagram?
MOSFET
Which circuit component is represented by the following diagram?
Capacitor
What will be the voltage across a capacitor when it is fully discharged?
Zero volts.
What is the annual effective dose of the average annual background radiation in the UK?
2.2mSv
What is meant by the activity of a source?
It is the number of decays/disintegrations per second
What is meant by gravitational field strength?
Force per unit mass
What is the charge on a proton?
Positive
Which device measures current?
Ammeter
State a device that can be used in a light sensor
LDR
State 2 issues that must be overcome in fusion reactors.
- The high temperatures required
- The high pressures required
How can you work out the resultant force acting on a space rocket at launch?
Resultant force = Engine thrust - (Weight + frictional forces)
What is DC?
Direct current. Electrons move in one direction only.
What is the symbol for a voltmeter?
Circle with a V in it
For a projectile fired horizontally, what would the horizontal velocity time graph look like?
Constant horizontal velocity - therefore a straight horizontal line.
What effect does a convex lens have on light rays?
The light rays converge to a focal point, by refraction of the light.
Explain how a seatbelt works in terms of Newton’s Laws.
- When a car travels at a constant velocity the forces on it are balanced. (Newtons 1st Law)
- If the brakes are applied they provide an unbalanced force that stops the car. (Newtons 2nd Law)
- The passengers continue to travel at a constant speed in a straight line. (Newtons 1st Law)
- The seatbelt provides an unbalanced backwards force to decelerate the passenger to zero without hitting the windscreen. (Newtons 2nd Law)
What is the fuel in a nuclear fission reactor?
Uranium
State one detector of visible light.
- Retina in the eye,
- photographic film
A car is travelling at a constant velocity of 25ms-1, the engine is producing a force of 4000N. What is the size of the frictional forces acting on the car?
4000N backwards
What is the rule for current in a series circuit?
The current is the same everywhere
How does a relay work?
- Close a switch to make a current flow in a wire.
- This creates an electromagnet.
- Electromagnet attracts metal switch.
- This completes the second circuit and the lamp switches on.
Describe an experiment to investigate the relationship between the temperature and the pressure of a fixed mass of gas, with a fixed volume.
- Place the flask in a beaker of water.
- Heat the water.
- As the water heats up take a set of readings.
- The temperature of the water from the thermometer
- The pressure of the gas from the bourdon gauge
- Draw graph of pressure against temperature
State one source of gamma radiation
- Stars
- Some radioactive substances (e.g. Cobalt 60)
What does an electric field line show?
The direction a positive charge would move in that field.
What is the energy change in a photovoltaic cell?
Light to electrical
What is meant by refraction?
Refraction is the change of speed of light as it enters a different medium - often observed as a change in direction.
How is the period of a satellite effected by the orbiting altitude/height?
The bigger the orbiting altitude / height the longer the period orbit.
How can a space rocket be slowed down in space?
Reverse the thrusters to provide an unbalanced force backwards to slow you down.
State one source of gamma radiation
- Stars
- Some radioactive substances (e.g. Cobalt 60)
If you heat a conductor, what happens to it’s resistance?
It increases
What temperature does absolute zero occur at?
0 K or -273 OC.
What type of spectrum is this?
Continuous spectrum
Which circuit component is represented by the following diagram?
Diode
State one use for radio waves.
- Radio/TV broadcasting
- Aircraft and shipping bands
- Radio waves detected from space are used by astronomers to find out what objects are made from
Explain the difference between average and instantaneous speed.
Average speed is over a long period of time, Instantaneous speed is the speed over a very short period of time.
How is a uniform electric field represented?
Evenly spaced field lines
What are the forces acting on a space rocket at launch?
- Weight - downwards
- Friction/air resistance - downwards
- Engine thrust upwards
What type of wave is a microwave?
Transverse.
Explain how snow shoes prevent you sinking into the snow.
Snow shoes have a large area. So the force of the person (weight) is spread over a larger area so the pressure exterted on the snow is less as P = F/A
What is electric charge?
An electric charge occurs when there are fewer or more electrons than protons.
What is the estimated age of the universe?
14 billion years
Explain how a radiation film badge is used to monitor the exposure to radiation.
- Badge has several windows in it made from different materials - when the film is developed the type of radiation can be identified by which windows have been penetrated by the radiation
- The darker the film behind the windows the more radiation the badge has been exposed to.
What is meant by the critical angle?
The angle of incidence that gives an angle of refraction of ninety degrees.
Red lines on diagram illustrate this.
Describe how to calculate acceleration from a veocity - time graph.
- Pick two pints on the slope.
- u = initial speed-read it off the graph,
- v = final speed-read it off the graph,
- t = time to go from the initial to the final speed.
- Then use a = (v-u)/t
What is the energy change in a motor?
Electrical to kinetic
What is meant by an acceleration of 15ms-2 ?
The velocity increases by 15ms-1 every second.
What is a fuse?
Safety device that protects the flex
What is the symbol for a voltmeter?
Circle with a V in it
What is the energy change in a loudspeaker?
Electrical to sound
Name 3 transverse waves.
- Radio
- Microwave
- Infrared
- Visible light
- Ultraviolet
- X-rays
- Gamma rays
- Water waves
What is the shape of a concave lens?
See image
State one detector of Ultraviolet light.
- Some chemicals glow or fluoresce under it
- photocells
What happens if two positive charges are brought together?
They repel each other
In the hills you can sometimes pick up a radio signal but not a television signal?
Radio waves are longer wavelengths than television waves.
Radio waves diffract more and can reach the receiver.
An object travels at a constant speed of 10ms-1. What can be said about the forces on it?
The forces are balanced
What is the difference in the diffraction pattern produced by waves passing through a wide and a narrow gap? (Wavelength is the same)
The narrower the gap, the more diffraction that occurs.
In an atom which particle orbits the nucleus?
Electron
State one use for gamma radiation.
- Used as a tracer in medicine
- Used to treat cancer
- Sterilisation of operating instruments
- In industry, radioactive “tracer” substances can be put into pipes and machinery, then we can detect where the substances go.
- Gamma rays kill microbes, and are used to so that it will keep fresh for longer. This is known as “irradiated” food.
- Checking for cracks in aeroplane wings and joints
What happens if you increase the resistance in a circuit?
The current will decrease
Name three scalar quantities
- Distance
- Time
- Speed
- Mass
- Energy
Suggest a way that we say ‘energy is lost’ (not converted to the type of energy we want)?
- Heat lost to the surroundings due to friction
- Sound energy lost to air because of vibrations
- Energy lost as heat to the surroundings
- Heat lost in heating up a container instead of the substance in it
What would happen to an electron being fired through the electric field below?
It would experience a force and be attracted to the positive plate.
What is meant by a light year?
The distance that light could travel in one year.
What does this velocity-time graph show?
Constant acceleration
Which circuit component is represented by the following diagram?
Light Emitting Diode
What type of current is represented by this oscilloscope image?
DC
What happens if two negative charges are brought together?
They repel each other
Which particles are in the nucleus of the atom?
Protons and Neutrons
State a source of natural background radiation.
1) Rocks: Some rocks such as granite or pitchblende are high in radioactivity
2) Food: Food can be slightly radioactive because of the soil it has been grown in.
3) Body: Contains Potassium 40 which is radioactive.
4) Cosmic Rays: Radiation from the Sun and outer space. The atmosphere will absorb most of this.
5) Radioactive gases: Radon and Thoron gases make up most of the dosage you will receive from background radiation. The gases come from rocks underground and the amount you are exposed to depends on the geology of where you live.
What is meant by the potential difference (voltage) of a supply?
It is the number of Joules of energy given to each coulomb of charge passing through the cell
Give an advantage of producing electricity using a nuclear fission reactor.
- Do not produce greenhouse gases – Carbon dioxide, methane, nitrous oxide
- Do not rely on fossil fuels which are in short supply
- Huge amount of energy from a small amount of fuel
- Small amount of waste produced
- Reliable source of energy (Unlike solar or wind)
These two block of wood have identical mass. Explain which exerts the greatest pressure.
- Both blocks have the same mass, so as W=mg will exert the same force down on the surface.
- Block B is sitting so that a small area sits on the surface, so as P = F/A it will exert a larger pressure.
What is the difference between a vector and a scalar quantity?
A scalar needs size/magnitude to be described correctly. A vector needs size/ magnitude and direction to be described correctly.
How does light travel through an optical fibre?
It travels by Total Internal Reflection
What is meant by the wavelength of a wave?
It is the distance from a point on one wave to the same point on the next.
An astronaut has a mass of 50kg. What will happen to the astronauts weight on the Moon?
The weight will decrease as there is a lower gravitaional field strength on the Moon.
State one detector of microwaves.
Aerial
An astronaut has a mass of 50kg. What will happen to the astronauts mass on the Moon?
It stays at 50kg. Mass does not change.
What would the field lines around a positive point charge look like?
Field lines show direction away from the positive point charge.
What will an unbalanced force cause?
Acceleration
What is the stated value of the mains?
230V, 50Hz
What are the issues of potential exposure to radiation?
Can cause
- cataracts
- increased risk of cancer
- damage to DNA and genetic material
What is the energy change in a loudspeaker?
Electrical to sound
What does the area under the velocity-time graph give?
The distance travelled
What is the energy change in a microphone?
Sound to electrical
What happens if you unscrew one of the lamps in the circuit below? Why?
The other lamps go out. There is a break in the circuit and the current does not have a complete route to the battery.
How can you identify a series circuit?
It is a circuit with only one path round it.
Describe an experiment to investigate the relationship between the the pressure and the volume of a fixed mass of gas, at a constant temperature.
Boyles Law:
- Pump is used to put pressure on oil which puts pressure on a fixed mass of trapped gas.
- Valve is closed.
- Volume of air column is read off the scale.
- Pressure is read off the bourdon gauge.
- Valve is opened and closed to change the pressure to get a set of readings.
- Draw graph of pressure against volume.
Which circuit component is represented by the following diagram?
Photovoltaic cell / solar cell
State one method of monitoring exposure to radiation.
Radiation film badge.
What is the rule for voltages in a parallel circuit?
The voltage across each branch is equal to the supply voltage.
What is an exoplanet?
A planet orbiting a sun outside our solar system.
Which circuit component is represented by the following diagram?
Light Dependent Resistor
What is the rule for voltages in a series circuit?
The voltage across each component added together is equal to the supply voltage.
Explain how a skydiver reaches terminal velocity.
- When the skydiver jumps out of a plane his initial vertical velocity is zero.
- His weight causes him to accelerate towards the ground. (Weight = Force = ma)
- As the skydivers velocity increases the air resistance upwards increases too.
- So the unbalanced force down becomes less, so there is less aceleration towards the ground. (Weight - air resistance = Unbalanced Force = ma)
- Eventually the weight downwards is equal and opposite to the air resistance upwards.
- This is a balanced force so the skydiver reaches terminal velocity.
What type of current is represented by this oscilloscope image?
DC
What is the energy change in an LED?
Electrical to light
Which circuit component is represented by the following diagram?
Lamp
What is a planet?
A ball of mass that
- orbits a sun
- has enough mass to be almost round
- is not a moon of another object
- has removed debris from the area round the orbit
State one use for visible light.
- We use light to see!
- Lasers are visible light and are used in Xbox, Playstation, Bluray player, DVD (where the light is reflected from the tiny pits in the disc, and the pattern is detected and translated into sound or data)
- Lasers also used in laser printers
- In aircraft weapon aiming systems.
What is the function of a MOSFET?
Electronic switch
State a device that can be used in a temperature sensor
Thermistor
What is acceleration?
Acceleration is the rate of change of velocity or the change in velocity per second.
Which circuit component is represented by the following diagram?
Microphone
What two factors effect the running cost of an appliance?
The time it is used for The power rating of the appliance
What does this velocity-time graph show?
Constant velocity
What is the energy change in a buzzer?
Electrical to sound
Explain how electrostatics can be used in paint spraying a car.
Car is connected to a negative terminal so that it is negatively charged.
Spray gun is made positively charged so the paint particles are positive.
The poistive paint is attracted to the negative car.
Areas of the car already covered in paint will repel any more charged paint.
Using Kinetic Theory explain what happens to the pressure if you increase the temperature of a fixed mass gas in a fixed volume container?
- Pressure is caused by the force of particles hitting the sides of the container.
- The temperature is increased. The particles gain kinetic energy.
- They will move faster and so hit the sides of the container more often and with a greater velocity so increasing the force.
- So the pressure increases.
What happens if two negative charges are brought together?
They repel each other
What is meant by fusion?
Fusion is when two nuclei of smaller mass number combine to form a nucleus of larger mass number.
When would you use a relay?
To switch on a high current ciruit using a low current circuit for safety.
What is meant by streamlining?
Streamlining is changing the shape of an object to reduce air/water resistance
How can the issue of manoeuvring in space be overcome?
Use of reverse thrusters.
Name one place that electrostatics can be used.
- Laser printers
- Paints spraying
- Cling film
- Forensic science
- Dust removal
- Electrostatic precipitators
- Electrostatic separators
Name the members of the electromagnetic spectrum, from lowest to highest frequency.
(Ronald Mcdonald Is Very Ugly eXclaimed George)
- Radio
- Microwave
- Infrared
- Visible Light
- Ultraviolet
- X-rays
- Gamma radiation
How can a parallel circuit be identified?
It is a circuit with more than one path round it.
Which circuit component is represented by the following diagram?
Variable Resistor
What is the symbol for an Ohmmeter?
Circle with an Omega in it
What happens if a positive and a negative charge are brought together?
They attract each other
What is the difference between real and apparent depth? Explain how this happens.
We think that the water is shallower than it actually is. (apparent depth)
This is because
- The light is refracted at the water/air boundary and changes direction away from the normal
- Our eyes/brain assume that light travels in straight lines.
What is a dwarf planet?
A dwarf planet
- Orbits a sun
- has enough mass to be almost round
- is not a moon of another object
- HAS NOT removed debris around area of the orbit
What is meant by a chain reaction?
A chain reaction is when a neutrons causes fission and releases more neutrons. The neutrons produced in the fission reaction, go on to cause their own fission reactions.
What is the difference in the two waves shown below?
The top wave has a bigger amplitude and so has more energy.
(Or the bottom wave has a smaller amplitude so has less energy)
What is the shape of a convex lens.
See image
What is meant by the ‘normal’?
An imaginary line drawn at ninety degrees to the surface that all angles are measured from.
Which line on the graph represents the largest acceleration?
Blue Line - it has the steepest gradient
Which circuit component is represented by the following diagram?
Switch
Explain how a satellite stays in orbit.
Satellite has a constant horizontal velocity.
Satellite has a constant vertical acceleration due to the gravitational field strength of the planet.
This gives a curved trajectory.
The planet is curved so the satellite remains in orbit.
Which circuit component is represented by the following diagram?
Motor
Describe how to measure the speed of sound using the equipment below.
- Make a loud sound to the left of the first microphone.
- When the sound reaches microphone one it starts the fast timer, when the sound reaches the second microphone this stops the timer.
- Measure the distance between the microphones using a metre stick.
- The speed is calculated from distance between the microphones divided by the time on fast timer.
What will the amount of shielding required depend on?
The amount of shielding required to protect against different kinds of radiation depends on how much energy they have.
What is the radiation known as beta radiation?
It is a fast moving electron from the nucleus.
Describe how to measure average speed using the equipment below.
- Two light gates are connected to a timer.
- The car rolls down the slope.
- When the cardboard breaks the first lightgate beam it starts the timer. When the cardboard breaks the second lightgate beam it stops the timer.
- The timer records the time taken to go from the first to the second light gate.
- Measure the distance between the two light gates using a metre stick.
- Calculate the speed = distance between light gates / time on timer
For a projectile fired horizontally, what would the vertical velocity time graph look like?
It would show a constant acceleration, a line of gradient = 9.8ms-2
Where does the energy come from in a fission and a fusion reaction?
Some of the mass is converted into energy.
How can power losses be reduced in transmission lines?
By increasing the transmission voltage and so decreasing teh transmission current. Power loss P = I2R, so if the current is reduced the power lost is reduced.
What causes friction?
Two surfaces rubbing together
Which circuit component is represented by the following diagram?
Capacitor
What is meant by temperature?
It is a measure of the mean kinetic energy of the particles.
What is the difference in the two waves shown below?
The bottom wave has a higher frequency. (Or the top wave has a lower frequency)
What is meant by ionisation?
It is when an atom gains or loses an electron to become charged.
Which circuit component is represented by the following diagram?
Variable Resistor
Describe how to measure average speed.
- Mark a start line and a finish line.
- Measure the distance between the start and finish line with a ruler/metre stick.
- Start a stopwatch when the object crosses the start line and stop it when the object crosses the finish line.
- Calculate the average speed = distance between start and finish / time on stopwatch
Which circuit component is represented by the following diagram?
Motor
What is the symbol for an ammeter?
Circle with an A in it.
What is meant by absorbed dose?
The energy absorbed per unit mass
What is meant by the frequency of a wave?
The number of waves per second.
State an advantage of a fusion reactor.
- Releases massive amounts of energy
- It is sustainable (unlikely to run out)
- No greenhouse gases
- No risk of meltdown
What type of spectrum is this?
Line Spectrum
State one source of radio waves.
- Transmitter
- Stars
State one way that travelling the large distance in space could be overcome.
- Use an ion drive
- Gravity assist (catapult) from a planet, moon or fast moving asteroid
How does is the frequency of a wave related to it’s energy?
The higher the frequency the more energy the wave has.
What is meant by the amplitude of a wave?
It is the distance from the centre of the wave to the crest or trough.
What is meant by diffraction?
It is the bending of waves round an object.
How does the observable universe let us estimate the age of the universe?
The furthest point that we can detect is the distance which light must have travelled for the whole age of the universe.
This allows us to work out the approximate time of travel and so teh age of the universe.
What precautions should be taken when storing a radioactive source?
- Source should be clearly labelled as to type
- Stored in lead lined boxes
What is the rule for current in a parallel circuit?
The supply current is equal to the current in each branch added together.
State one source of X-rays.
- Stars
- Nebula
What are the particles in the nucleus called?
Protons and neutrons
Which circuit component is represented by the following diagram?
Cell
Which circuit component is represented by the following diagram?
Lamp
State one detector of radio waves.
Aerial
If you heat a conductor, what happens to it’s resistance?
It increases
State one source of microwaves.
- Transmitter
- Magnetron
What path will the ray of light take as it passes through the glass prism?
Light ray is refracted at air/glass boundary and glass/ air boundary. Both result in a change of direction.
As it enters the block the speed of the light decreases and it changes direction towards the normal.
As it leaves the block the speed of the light increases and it changes direction away from the normal.
State one use for infrared radiation.
- Skin emits infrared light we can be seen in the dark by someone using night vision goggles.
- Astronomers use infrared to give extra information about space. Infrared light maps the dust between stars.
- Can be used to create thermograms which are used in medicine as a diagnostic tool for cancer, deep vein thrombosis(DVT), circulation problems (Reynaulds syndrome)
- Remote controls for TVs, DVD, Bluray players etc
- Physiotherapists use heat lamps to help heal sports injuries
What do waves transfer?
Energy
How can you indicate a weaker electric field?
Less field lines
What is a geostationary satellite?
Satellites with a period of 24 hours and orbit at a height of 36000km.
Give a disadvantage of producing electricity using a nuclear fission reactor.
- The waste produced is radioactive. It has to be stored safely for a long time.
- Uranium is a non-renewable fuel.
- Risk of radioactive materials being released into the environment if there is an accident.
- Expensive to decommission nuclear power stations at the end of their useful life.
You are 10km from a thunder storm. You count 15 seconds between seeing the lightning and hearing the thunder. How do you calculate how far away the storm is?
Use d = vt
Where v is the speed of sound.
t is 15 seconds.
State one use for microwave radiation.
- Mobile phone communications
- Used to heat/cook food
- Microwaves in space are used by astronomers to learn about the structure of nearby galaxies, and our own Milky Way
- Microwaves are also used by fixed traffic
- Radar
How should a diode or LED be connected with a battery to light correctly?
Small line on battery points to small line on LED or diode.
What is the rule for selecting a fuse from a power rating?
Appliances less than 720W use a 3A fuse Appliances more than 720W use a 13A fuse
What is the energy change in a buzzer?
Electrical to sound
What is the rule for current in a parallel circuit?
The supply current is equal to the current in each branch added together.
What is a Light Dependent Resistor?
A resistor whose resistance changes with changes in light level
List some benefits of space exploration.
- Satellite communications
- GPS and SatNav technologies
- Weather forecasting / storm tracking
- Improved mapping
- Spin off technologies - hand held drills, portable DVD players, memory foam
- Space exploration e.g Hubble telescope, International space station
Two 1kg blocks of metal are heated up. Block A and Block B. Each block is made from a different material. They are both supplied with 10000J on energy. Block B has the biggest temperature change.
What can you say about Block B compared to Block A?
Block B has a lower specific heat capacity.
What is specific heat capacity?
The number of Joules of energy needed to raise 1kg of a substance by 1OC.
What is the difference between speed and velocity?
Speed is a scalar and is equal to distance divided by time. Velocity is a vector and is displacement divided by time, with a direction.
Explain how a fuse works.
A fuse is a thin wire. If too much current passes through it, it will get hot and melt. This breaks the circuit.
Which circuit component is represented by the following diagram?
Transistor
Explain why re-entering the atmosphere poses a challenge.
- When a space craft is in space there is no friction as space is a vacuum.
- When you re-enter the Earth’s atmosphere you go from no friction to lots of friction (caused by the atmosphere).
- The result is that the space craft loses kinetic energy and slows down.
- However due to conservation of energy, the energy is not lost but is converted to heat.
- The outside of the space craft becomes incredibly hot.
- This means that the space vehicle requires thermal shielding.
What is meant by background radiation?
It is the radiation that is all around us.
What is the energy change in an LED?
Electrical to light
Explain how to measure acceleration using the equipment shown below and a stop watch.
- When the cardboard passes through the first light gate the timer attached to it records this time.
- Measure the length of the card with a ruler.
- The initial velocity, u = length of card / time on timer
- As the car rolls down the ramp, start the stop watch when it reaches the first light gate and when it reaches the second light gate stop the stop watch.
- This is t, the time for the change in velocity.
- When the cardboard passes through the second light gate the timer attached to it records this time.
- The final velocity, v = length of card / time on timer
- Then calculate acceleration, a = (v-u)/t
How can the electromagnetic spectrum be used to obtain information about objects in space?
Different objects in space emit different signals that we can detect to get information about the object.
Different frequencies require different detectors.
What is a thermistor?
A resistor whose resistance changes with changes in temperature
Which colour of light is refracted least in a triangular prism when white light is shone through it?
Red light
When would you use a relay?
To switch on a high current ciruit using a low current circuit for safety.
State one source of ultraviolet light.
- Sun
- Special Lamps
What is meant by heat?
It is the energy of the substance.
What is meant by absolute zero?
- When gas particles have no energy and cannot move or collide with the sides of the container.
- They have no more kinetic energy to remove.
- Temperature cannot go below this.
What is the function of a MOSFET?
Electronic switch
Describe a streamlined shape
- Low to the ground
- Smooth
- Have curves
How should an ammeter be connected to measure the current in a component?
It should be connected in series with the component
What does the area under this velocity time graph give?
If positive area and negative area are subtracted it gives the displacement. If the total area is calculated it gives the distance travelled.
Which circuit component is represented by the following diagram?
Switch
What is a sun?
A star is called a sun if it is the centre of a planetary system.
What is the charge on an electron?
Negative
What would happen to an electron being fired through the electric field below?
It would experience a force and be attracted to the positive plate.
What is the effect of an electric field on a charge?
The charge will experience a force.
Which circuit component is represented by the following diagram?
Photovoltaic cell / solar cell
What would the field lines around a negative point charge look like?
Field lines show direction towards the negative point charge
How should an ammeter be connected to measure the current in a component?
It should be connected in series with the component
Which device measures voltage?
Voltmeter
How can you indicate a weaker electric field?
Less field lines
Which circuit component is represented by the following diagram?
Fuse
When is work done?
When a force is exterted over a certain distance.
Using Kinetic Theory explain what happens to the volume if you increase the temperature of a fixed mass gas at a fixed pressure?
- Pressure is caused by the force of particles hitting the sides of the container.
- The temperature is increased. The particles gain kinetic energy.
- They will move faster and so hit the sides of the container more often and with a greater velocity and so greater force.
- So the pressure increases.
- This puts pressure on a rubber bung/bead of mercury etc. and it moves. It will move until the pressure inside the container = pressure outside the container.
- So the volume will increase.
Which device measures resistance?
Ohmmeter
What is the rule for voltages in a series circuit?
The voltage across each component added together is equal to the supply voltage.
What type of wave is a water wave?
Transverse.
What is electric charge?
An electric charge occurs when there are fewer or more electrons than protons.
For the diagram of the atom name the parts.
How can you calculate the distance that is one light year?
- d=vt
- d = 3 x 108 x (365.25 x 24 x 60 x 60)
What is the annual effective dose limit for a radiation worker?
20mSv
What does the gradient of the line on velocity - time graph represent?
The acceleration
Which circuit component is represented by the following diagram?
Thermistor
When does an object have kinetic energy?
When it is moving.
What are the possible dangers of space exploration?
- pressure differential
- exposure to radiation
- fuel load on take-off
- re-entry through atmosphere
In the diagram below, where is;
- the normal ?
- the angle of incidence?
- the angle or refraction?
See diagram
What is current?
The charge transferred per second
What causes pressure of a gas in a container?
Gas particles hitting the sides of a container
Explain an experiment to measure the half life of a source.
- With no source present record the number of counts in one minute using the G-M tube and counter. This is the ‘background radiation’.
- Put source in position. The stop clock and the counter are started at the same time.
- Take a reading of the counts per minute every minute. Do this for 10 minutes.
- The background radiation is subtracted from each of the readings so that the counts / minute for the source are recorded.
- A graph is plotted of counts / minute against time. The half-life is calculated from the graph.
State one use for ultraviolet radiation.
- UV lamp in a chip shops. (The UV attracts insects, which are electrocuted by high-voltage wires near the lamp - so they won’t land on the food and contaminate it.)
- Detecting forged bank notes in shops (security markings fluoresce under UV light)
- Hardening some dental fillings
- Night club lighting
- UV security pens to mark property
- Killing microbes – Sterilising surgical equipment, air in operating theatres
- Food and drug companies use UV lamps to sterilise products
- Used by the body to produce vitamin D
- Doctors can use it to treat Vitamin D deficiency, acne etc.
Which member of the electromagnetic spectrum has the most energy?
Gamma radiation as it has the highest frequency
What is the rule for selecting a fuse from a power rating?
Appliances less than 720W use a 3A fuse Appliances more than 720W use a 13A fuse
What is meant by a longitudinal wave?
A wave that vibrates along the direction of travel.In a longitudinal wave, the motion of the medium is parallel to the direction of the wave.
What is the impact of ionisation on living cells?
It can kill them.
What is the effect of an electric field on a charge?
The charge will experience a force.
Using Newton’s 3rd Law explain how a space rocket takes off.
Engines push exhaust gases downwards. Exhaust gases push engines upwards.
What is meant by the universe?
The universe is all of time and space and its contents.
Newtons 1st Law is about balanced forces, what two things can happen if a balanced force acts on an object?
- Remains stationary
- Travels at a constant speed in a straight line
Why is containment an issue for fusion reactors?
The high temperatures of the plasma would vapourise any materials that we currently know.
What is meant by pressure?
The force per unit area
State two place a variable resistor can be used.
Light dimmer switch sped control on Scalextric cars volume control on a radio
What does a capacitor do?
Stores charge or energy
What is the energy change in a microphone?
Sound to electrical
What is the stated value of the mains?
230V, 50Hz
What happens if a positive and a negative charge are brought together?
They attract each other
What is meant by a transverse wave?
A wave that vibrates at ninety degrees to the direction of travel. A transverse wave is a wave in which the motion of the medium is at right angles to the direction of the wave.
What type of current is represented by this oscilloscope image?
AC
Which wave property is illustrated in the diagram below?
The amplitude of a wave.
What happens if you unscrew one of the lamps in the circuit below? Why?
The other lamps go out. There is a break in the circuit and the current does not have a complete route to the battery.
Which circuit component is represented by the following diagram?
Battery
Which is the least ionising radiation?
Gamma
What is meant by shielding?
Shielding means having something that will absorb radiation between you and the source of the radiation.
A temperature - time graph is shown below. What is happening at point B on the graph?
- The material is changing state.
- From solid to liquid
What happens to the speed of light as it travels from air into glass?
The speed of light in glass is slower than the speed of light in air.
State one source of infrared.
- Stars
- Lamps
- Flames
What is the energy change in a motor?
Electrical to kinetic
Give at least 2 uses for radiation.
- Gamma rays are used for radiotherapy which is a cancer treatment
- Thickness control of paper or metal sheet for example.
- Gamma radiation can be used to sterilise medical instruments
- Radio-carbon dating
- Tracers - can be used in industry in pipes to look for cracks or in the human body to check for blockages
What is the charge on a neutron?
No charge
What is the function of a transistor?
Electronic switch
State one detector of infrared
- photodiode
- phototransistor
If an object is projected horizontally from a cliff, how can the height of the cliff be calculated?
- Sketch a vertical velocity-time graph
- Due to gravitational field strength the velocity will increase vertically by 9.8ms-1.
- Calculate the area under the velocity-time this is equal to the verical height of the cliff.
You are 10km from a thunder storm. You count 15 seconds between seeing the lightning and hearing the thunder. You repeat this after the next lightning strike, the time between the lightning and the thunder is now 10 seconds. What does this tell you?
The storm has moved closer to you.
State a device that can be used in a light sensor
LDR
How can a parallel circuit be identified?
It is a circuit with more than one path round it.
Which device measures resistance?
Ohmmeter
Does a light ray always change direction when it undergoes refraction?
No.
What is the annual effective dose limit for a member of the public?
1mSv
Which circuit component is represented by the following diagram?
Fuse
Explain how a satellite stays in orbit.
Satellite has a constant horizontal velocity.
Satellite has a constant vertical acceleration due to the gravitational field strength of the planet.
This gives a curved trajectory.
The planet is curved so the satellite remains in orbit.
What effect does a concave lens have on light rays?
It causes them to diverge - by refraction of the light
What is the energy change in a buzzer?
Electrical to sound
What happens if two positive charges are brought together?
They repel each other
What is power?
The energy used per second
What is the rule for current in a series circuit?
The current is the same everywhere
You are 5km away from a thunder storm. What reaches you first - the thunder or the lighning? Explain your answer.
The lightning. The speed of light is faster than the speed of sound.
What is meant by a corrected count rate?
It is when the background radiation is subtracted from the radiation measured so that the reading is caused by the source not background radiation.
Explain how a fuse works.
A fuse is a thin wire. If too much current passes through it, it will get hot and melt. This breaks the circuit.
Which circuit component is represented by the following diagram?
Microphone
What is the charge on a neutron?
No charge
Which circuit component is represented by the following diagram?
Cell
How can you reduce your exposure to radiation when you are working with it?
- Limit the time you have the source out (only get it when you need it)
- Handle only using tongs
- Keep the source at arm’s length
- Wash hands before and after use
- Do not eat while handling it
- Wear lead lined gloves/apron and safety goggles
What is DC?
Direct current. Electrons move in one direction only.
What is Newton’s 3rd Law?
For every action force there is an equal but opposite reaction force
Name one place that electrostatics can be used.
- Laser printers
- Paints spraying
- Cling film
- Forensic science
- Dust removal
- Electrostatic precipitators
- Electrostatic separators
What is a solar system?
It is a system bound by gravity, made up of a sun and the objects that orbit it.
What would the field lines look between parallel plates?
Field lines run from positive to negative plate, with a bulge at the ends of the parallel plate.
Which circuit component is represented by the following diagram?
Resistor
The graph below shows a temperature - time graph. Points B and D show changes in state. Explain why this can be identified from the graph.
When a substance changes state the temperature remains constant. (Shown by horizontal line on graph)
Which device measures voltage?
Voltmeter
How can you increases friction?
- Increase the area of the rubbing surfaces
- Make the rubbing surfaces rougher
- Push the rubbing surfaces togerther more
- Increase the speed that the surafces are rubbed together
How should a voltmeter be connected to measure the voltage across a component?
It should be connected across the component
What is the charge on a beta particle?
Negative
What is the difference between distance and displacement?
Distance is the length of the path you actually take and it is a scalar, displacement is the straight line distance between where you started and finished including a direction as it is a vector.
What is the charge on an electron?
Negative
What are the products in a fission reaction in a nuclear reactor.
- fission fragments (smaller mass nucleii)
- Heat energy
- More neutrons
Name one source of DC
Battery
What are the three types of radiation?
- alpha
- beta
- gamma
Which circuit component is represented by the following diagram?
Battery
Which component does the symbol represent?
Buzzer
How can you convert between OC (degrees Celsius) and K (Kelvin)?
Temperature in degrees Celsius + 273
Which is the most ionising radiation?
alpha
Which circuit component is represented by the following diagram?
Light Emitting Diode
How can you indicate a stronger electric field?
More field lines
What is the energy change in a buzzer?
Electrical to sound
What would the field lines around a negative point charge look like?
Field lines show direction towards the negative point charge
State one detector of gamma radiation
- Photographic film
- GM Tube
- Bubble chamber
How can you decrease friction?
- Decrease the area of the rubbing surfaces
- Make the rubbing surfaces smoother
- Push the rubbing surfaces together less
- Decrease the speed that the surfaces are rubbed together
- Lubricate/oil/ wax the surfaces
- Streamline the object
What is AC?
Alternating current. The electrons change direction, moving backwards and forwards, many times in a second.
What is equivalent dose?
It is a way of taking into account the absorbed dose and the type of radiation you are exposed to.
What are the two main challenges of re-entry?
- Angle of re-entry
- High temperatures / heating effect
Explain why a projectile follows a curved trajectory.
- It has a constant horizontal velocity
- It has a constant vertical acceleration downwards due to gravity
State one detector of X-rays
Photographic film
Describe how to measure the speed of sound with two students using a clapper board, stop watch and trundle wheel.
- One student takes the clapperboard and stands still.
- The other students takes the stop watch and uses the trundle wheel to measure a set distance away.
- The first student shuts the clapper board.
- The other student starts the stop watch when they see the clapper shut and stops it when they hear the sound.
- Speed of sound is calculated by distance between the students divided by the time on stop watch.
What are the main parts of an atom?
See diagram
What is the energy change in a photovoltaic cell?
Light to electrical
State the equipment you would need to measure the half life of a source.
- Timer
- G-M Tube and counter
- Source of radiation
What is the charge on an alpha particle?
Positive
What two factors effect the running cost of an appliance?
The time it is used for The power rating of the appliance
Which colour of light is refracted most in a triangular prism when white light is shone through it?
Blue light
What will absorb gamma radiation?
Several centimetres of lead
When does an object have potential energy?
When it is lifted through a height.
What does an electric field line show?
The direction a positive charge would move in that field.
Name one source of DC
Battery
State a device that can be used in a temperature sensor
Thermistor
What is the charge on a proton?
Positive
What happens when white light is shone through a triangular prism as shown?
The light is refracted and produces a spectrum.
What does a capacitor do?
Stores charge or energy
How can a space rocket be slowed down in space?
Reverse the thrusters to provide an unbalanced force backwards to slow you down.
What is a Light Dependent Resistor?
A resistor whose resistance changes with changes in light level
State a source of man-made background radiation.
1) Weapons testing
2) Waste from the Nuclear industry
3) Medical uses: Having an X-ray, CT scan, barium meal etc.
What is velocity?
Displacement travelled per second.
What is current?
The charge transferred per second
What is the charge on a neutron?
No charge
Explain why being stood on by a stilletto heel is painful.
Stileto heels have very small areas. So the force of the person (weight) is spread over a very small area so the pressure exterted is high as P = F/A
What is conservation of energy?
Energy cannot be created or destroyed it can only be transferred from one type to another.
What will be the voltage across a capacitor when it is fully charged?
The supply voltage.
A temperature - time graph is shown below. What is happening at point C on the graph?
The temperature of the liquid is increasing.
Which device measures current?
Ammeter
Using Kinetic Theory explain what happens to the pressure if you decrease the volume of a fixed mass gas at a constant temperature?
- Pressure is caused by the force of particles hitting the sides of the container.
- The volume is decreased. The particles have less room to move about and so hit the sides of the container more often increasing the force on the container.
- So the pressure increases.
How can power losses be reduced in transmission lines?
By increasing the transmission voltage and so decreasing teh transmission current. Power loss P = I2R, so if the current is reduced the power lost is reduced.
For the diagram of the atom name the parts.
What is the energy change in a buzzer?
Electrical to sound
Explain how electrostatics can be used in paint spraying a car.
Car is connected to a negative terminal so that it is negatively charged.
Spray gun is made positively charged so the paint particles are positive.
The poistive paint is attracted to the negative car.
Areas of the car already covered in paint will repel any more charged paint.
What does this velocity - time graph show?
Constant de-acceleration
What is meant by the period of a wave?
The time it takes one wave to pass a point.
A temperature - time graph is shown below. What is happening at point A on the graph?
The temperature of the solid material is rising.
State two challenges of space exploration.
- Travelling the large distances
- Manoeuvring
- Maintaining energy
State three detectors of radiation.
- Photographic film
- GM Tube
- Scintillation counter
What path will the ray of light take as it passes through the glass prism?
Light ray still experiences a change of speed - it is still refracted but no directional change.
What are the issues with fuel load on take-off?
There is a massive amount of fuel being carried and a huge amount of heat is produced. This could lead to an explosion.
How can you tell from this oscilloscope image that this is AC?
The trace shows a change in direction
What is the difference between mass and weight?
Mass is a measure of the partcles that make an object up. Weight is a force caused by the gravitational field strength of a planet.
Describe how to calculate the half-life of a source from a graph.
* Choose a ‘nice’ starting value e.g. 20,000Bq.
- Find the ‘time’ that this happens at e.g. 0 Hours.
- Once a half life has passed the activity will be 20,000÷2 = 10,000Bq.
- Find the time that this happens at from the graph – 12 Hours.
- Calculate the time for the change is 12 – 0 = 12 hours
Why is manoeuvring in space such an issue?
There is no friction to slow down.
How can the issue in maintaining energy in space be overcome?
Use solar cells angled towards the Sun.
Which circuit component is represented by the following diagram?
Light Dependent Resistor
Why is an LED normally connected in series with a resistor?
Resistor is to protect the LED by limiting the current in the LED.
What is meant by capacitance?
Charge stored per unit volt
Describe an experiment to investigate the relationship bewteen the volume and the temperature of a fixed mass of gas at a fixed pressure.
- A fixed mass of gas is trapped by a bead of mercury
- Place the capilary tube, thermometer and ruler/scale into the beaker of water.
- Heat the water.
- At different temperatures - measure the temperature of the gas from the thermometer and the volume from the ruler/scale.
- The pressure is kept constant as the bead of mercury is free to move so that the pressure reamins constant.
- Plot a graph of volume against temperature.
What will be the voltage across a capacitor when it is fully charged?
The supply voltage.
Which particles are in the nucleus of the atom?
Protons and Neutrons
What is the energy change in a lamp?
Electrical to light (+ heat)
What is latent heat of fusion?
The number of Joules of energy required to change 1kg of a solid to 1kg of a liquid with no temperature change.
Explain the energy change as the sledge slides down the hill.
- At the start the sledge has potential energy.
- As it starts to slide down the hill it loses potential energy and gains kinetic energy
- At the bottom of the hill the sldge has no potential energy it has all been transferred to kinetic energy.
- At any point on the slope the potential energy + the kinetic energy = potential energy at the top of the slope.
What is AC?
Alternating current. The electrons change direction, moving backwards and forwards, many times in a second.
What happens to a light ray as it travels from air into glass?
It will slow down and change direction towards the normal.
What is a star?
A ball of gas undergoing fusion that gives off heat and light.
What is the function of a transistor?
Electronic switch
How does a nuclear fission power station produce electrical energy?
- The nuclear reactor uses fission of Uranium to produce large amounts of heat energy.
- The heat energy is used to heat water.
- The water which is heated, turns into steam, is piped to turn a turbine.
- The steam makes the turbine turn. (Heat energy to Kinetic Energy)
- The turbine turns the generator to create electrical energy. (Kinetic to Electrical energy)
What is meant by fission?
Fission is when a nucleus of a large mass number splits into two nuclei of smaller mass numbers, with the release of energy and neutrons.
Why does a triangular prism produce a spectrum from white light?
Different frequencies/colours of light refract by different amounts.
Which wave property is illustrated below?
Wavelength
What is a balanced force?
Equal forces acting in opposite directions
A temperature - time graph is shown below. What is happening at point D on the graph?
- The material is changing state
- From a liquid to a gas.
What information can be extracted from the spectral lines from a star?
The elements present in the star.
Describe what is meant by an AC current
A current whose instantaneous value and direction changes with time.
