Physics Equations And Knowledge Flashcards
Formula for when there is a time, charge and current
Q = It
What formula to use when given a voltage, resistance and current
V = IR
What is voltage directly proportional to?
Current and/or resistance
As there is more light the resistance of an LDR….
Decreases
As the temperature of an ntc thermistor increases the resistance….
Decreases
Properties of an ideal diode
Perfect conductor when forward current and V, zero resistance with infinite current and no threshold voltage, opposite for opposite direction, e.g. no threshold voltage
Current and voltage rules for series
Current of all components is the same, voltage is the sum of all components (ratio)
Current and voltage rules for parallel
Total current is the sum of all current of the components, voltage is the same throughout in parallel
What formula to use when you have energy, voltage and charge
E= QV
Equation when you have voltage, power and current and how can this be changed if we have resistance instead of voltage
P= IV, since V= IR, P=I²R
What is the formula for energy transfer from power
E = Pt which can be re-arranged into E=VIt or E= I²Rt
Difference between hard and soft magnetic materials
Magnetically hard objects are ones that can be permanently magnetised and soft ones are objects that can be temporarily magnetised
What is induced magnetism?
When an object gains magnetism due to being kept/put in a magnetic field
What is the magnetic effect of a current?
If a current is flowing through a conductor, it starts to behave like a magnetic and therefore the current carrying conductor gets magnetised due to it
Magnetic field lines around a straight wire
Circular magnetic field, as you go out the weaker the field gets
Magnetic field lines around a coil/solenoid
Creates a type of North and south pole, + side of the battery is the south Pole of the field, - north pole
What factors affect the magnetic field strength
Type of metal used, amount of current flowing through the wire and temperature of the wire, as current increases the strength increases, as temp increases the strength decreases
What is the difference between permanent magnets and electromagnets?
Electromagnets are types of magnet that have a field produced by an electric current, permanent magnets are types of magnets that are made from hard materials that create their own persistent magnetic field
If a wire carrying a current is in a magnetic field, what can it experience?
A force
What factors effect the direction of a force in a magnetic field
The direction of the external magnetic field and the current flow
What factors affect the magnitude of the force on a wire in a magnetic field?
Force increases when current increases or the strength of the magnetic field increases.
In Fleming left hand rule, what do each of the thumb, first finger and second finger represent?
Thumb - Movement of force
First finger - Direction of the field
Second finger - Current flow
What equation is used to find the force of a wire in a uniform magnetic field
F = BIL (Force = magnetic field strength x current x length of wire)
Factors affecting the magnitude of the force/moment produced in a motor
Number of turns in the coil, current in the coil, strength of magnetic field
What occurs in a dc motor?
The coil is attached to a split ring commutator that has a gap in it to stop current flow when the coil is vertical and allow it to spin
Uses of electromagnets?
Magnetic elevators to lift heavy objects, maglev trains or data storage, transformers etc
What is induced when a wire cuts magnetic field lines?
A voltage/ potential difference
Factors affecting magnitude of induced voltage?
Speed of movement, field strength. Turns in coil, as all increase so does the voltage
Factors affecting the direction of voltage induced
Direction of relative motion between field and conductor or direction of field lines themself
What factors affect the output voltage of an a.c. generator?
Number of turns in the coil, strength of magnetic filed and increasing the rate of rotation
How does an a.c. generator work?
A coil is rotated in a magnetic field, a current is induced as a voltage also is induced, as it rotates the direction of the induced voltage changes direction, hence changing the current, slip rings connect to the coil and external circuit so a current can flow in the external circuit.
Applications of electromagnetic induction
A.c generators, dynamos (bike lights), microphones, loudspeakers/ headphones - motor effect
What is a step up and step down transformer?
A transformer designed to increase voltage from its primary to secondary is a step up transformer, a step down one is the opposite
What is the voltage ratio in a transformer?
Vp/Vs = Np / Ns
What is a consequence of 100% efficiency in a transformer?
Total transfer of electrical power so VpIp = VsIs or Vp/Vs = Is/Ip
What is the need for high voltage in power transmission?
We use step up transformers to increase voltage to thousands of voltage as due to P=IV, if voltage increases then current may decrease for a specific power, then, due to lower current, this means thay the energy lost is much less as heat energy wasted through resistance is proportional to current squared.
How would you calculate an energy loss in a transformer circuit?
P = I²R where R is given
Equation linking speed, time and distance
Speed = distance/time
Equation linking velocity, change in displacement and time
Velocity = Change in displacement /time
Equation for acceleration with change in velocity and time.
Acceleration= change in velocity / time
What is the equation for average speed
Average speed = total distance / total time
What is the equation with v² and u² in?
V² - U² = 2as
True or false, is there only one type of force?
False
What are some examples of different types of forces?
Weight, normal reaction, drag (including air resistance), friction, magnetic, electrostatic, thrust, upthrust, lift and tension
What is the elastic limit?
The elastic limit of a material is the furthest point it can be stretched or deformed while being able to return to its previous shape
What is elastic and inelastic extension
Elastic extension is where you can stretch a material with it returning to its original shape whereas inelastic extension is where the shape will not return back to what it was originally
What is hookes law and give the equation.
Hookes law was that the extension of an elastic object is proportional to the force applied up to a certain point, the equation is F = kx
What is the limit of proportionality?
The limit of proportionality refers to the point beyond which Hookes law is no longer true when stretching a material.
What are the two variations of the equation for energy stored in a stretched string?
E = 1/2 x Fx or E = 1/2 x kx²
What is newtons first law?
A body will remain at rest or in a state of uniform motion in a straight line unless acted on by a resultant external force.
What does mass resist?
Change in motion(inertia)
What is newtons second law and what are the equations for it?
Newtons second law is F = ma and suggests that the rate of change of linear momentum is directly proportional to the external force applied on the body. Which gives F = change in momentum / time
What is newtons 3rd law?
If body A exerts a force on body B, then body B exerts an equal and opposite force of the same type on body A (every action has an equal and opposite reaction)
What is the difference between mass and weight?
Mass is constant and is scalar whereas weight can change and is dependent on the gravitational field strength and is a vector
What is the weight equation?
Weight = mass × gravitational field strength or W=mg
What happens in free fall?
A body will fall with acceleration equivalent to g
What factors affect air resistance?
The velocity at which the object is travelling at, the cross sectional area, the shape/surface of the body
How does terminal velocity come around and what forces are involved?
In free fall, objects accelerate downwards due to gravity, as speed/velocity increases, frictional forces such as air resistance and drag increase, at terminal velocity, the weight of an object due to g is balanced by the frictional forces as resultant = 0
What is the equation for momentum?
Momentum = mass x velocity or p=mv
What is and how do you do the law of conservation of momentum in one dimension
Momentum is conserved overall and therefore Total momentum = momentum before + momentum after
What is the equation between force and momentum?
Force = rate of change of momentum or Force = change in momentum / time
Equation between work and force and distance?
Work done = Force x distance moved in direction of force or W = Fs
What is the equation for gravitational potential energy
Ep=mgh
What is the equation for kinetic energy
Ek = 1/2 x mv²
What is the equation that links power, energy and time
E = Pt
What is the law of the conservation of energy?
Energy cannot be created or destroyed, only transferred
What is the equation for percentage efficiency?
Efficiency = (useful output/total input) x 100
What are thermal conductors and insulators, give examples
Thermal conductors are materials that are good conductors of thermal energy, the opposite for insulators. Example of thermal conductors are metals such as copper, thermal insulators can be things like air and wood
What factors affect the rate of conduction?
•Temp difference, Q proportional to temp difference.
•cross sectional area, Q proportional to Area
• length/distance heat must travel, Q proportional 1/L
• time, Q proportional time
What is the effect of temperature on density
As the temp of a fluid increases, the density decreases, the opposite occurs when the temp decreases.
What is fluid flow caused by density difference?
Due to hot fluids being less dense, they rise into cooler areas, as the fluids rise, they cool and so become denser again and begin to sink, allowing a flow (how hot air balloons rise)
What is thermal radiation viewed as?
Electromagnetic waves in the infrared region.
What is absorption and emission?
All bodies emit and absorb types of electromagnetic radiation, regardless of temp. Perfect bodies will absorb all radiation and since good absorbers are good emitters, it would be a perfect emitter too, wouldn’t reflect. White and shiny silver surfaces are the worst.
What are the factors that affect the rate of absorption and emission?
Colour/texture of surface, the temperature of the surface and the surface area
What is the effect of energy being transferred to or from an object on it’s temperature?
Heat transferred to an object raises its temperature(more internal energy) unless it’s going through a state change.
What is the equation for specific heat capacity?
C = E / (m x change in temp) or E =mc × change in temp
Where temp is in °C
Particle model of solids, liquids and gases
Solids arranged in regular pattern with particles very close together, vibrating around a fixed position, lowest energy.
Liquids arranged randomly with particles close together, moving around each other, second lowest energy
Gas particles arranged randomly and far apart, move quickly in all directions and have highest energy.
Explain properties of solids liquids and gases using particle theory.
Solids have a fixed shape and cannot flow or be compressed due to the particles being fixed and being too close together.
Liquids flow and take shape of a container as particles can move around each other, can’t be compressed however due to closeness of particles.
Gases flow and completely fill containers as particles move quickly in all directions, can be compressed as particles far apart.
Explain pressure and temperature in particle terms
Pressure is caused by the collisions between the particles and the container wall, temperature is the average kinetic energy of the particles.
Under constant temperature, what are the features of an ideal gas?
pV = constant and can be used to calculate stuff by doing p1V1 = p2V2 (Boyles law)
What is the melting point and boiling point?
Melting point is the temperature at which a solid turns into a liquid or vice versa. Boiling point is the temperature at which a liquid turns into a gas or vice versa
What is the latent heat of fusion or vaporisation?
Latent heat of fusion is the change in energy at a substances melting point (in order to change 1kg of a substance). Latent heat of vaporisation is the change in energy at a substances boiling point (in order to change the state of 1kg of the substance)
Equation for latent heat problems
Q = mL where Q is energy required, m is mass and L is specific latent heat of whichever you are using
Equation for density
Density = mass / volume
How could we experimentally find the density?
For irregular shape, measure volume by using a eureka can and volume of water displaced, for regular, measure volume by other means, measure mass on scale and use equation.
Compare densities of solids, liquids and gases.
Solids have high densities, liquids still have high densities but a bit less than solid forms (apart from water,l and gases are not very dense at all.
Equation for pressure (solid force)
Pressure = Force / area
Equation for pressure by a fluid (such as hydrostatic pressure, pressure caused by still water)
Pressure = h (height or depth of the liquid) x density × gravitational field strength
p = h × density x g
What do waves transfer energy without?
Transfer energy without a net transfer of matter
Differences between transverse and longitudinal waves?
Longitudinal require medium (e.g. sound) and transfer energy parallel to the direction of motion. Transverse waves move through anything without a medium (e.g. light) and transfer energy perpendicular to the direction of motion.
What is rarefaction and compression
Part on a longitudinal wave where the particles are spaced out, compression is opposite when all the particles are together.
Examples of waves?
Electromagnetic spectrum (GXULIMR) and sound
What is the period of a wave?
How long it takes for one cycle of a wave to take place
What is the amplitude of a wave?
Maximum oscillation from equilibrium position
What is the frequency of a wave?
Amount of waves passing a point in a given time period
What is the wavelength of a wave?
Distance between two points on successive waves.
Equation for frequency of a wave?
F = 1/ T (where t is the period)
Equation for wave speed with a distance and time?
Wave speed = distance / time
Equation for wave speed with a frequency and wavelength?
v = f × lamda or wave speed = frequency × wavelength
What is reflection of a wave?
Waves (including sound and light) can be reflected at a boundary between two different materials, this comes with the law that the angle of incidence = angle of reflection
What is refraction of a wave?
Refraction is the change in direction of a wave as it moves through a boundary.
What happens to the speed, frequency, wavelength and direction of waves in refraction
From a less denser medium to a more dense medium, the waves move slower and therefore have a shorter wavelength, this means the frequency doesn’t change and the waves move towards the normal, reverse the mediums reverses the effects.
What happens to the speed, frequency, wavelength and direction of the waves in reflection?
The speed stays the same along with the wavelength and frequency and the direction of the wave changes by the angle of incidence.
What is the doppler effect?
An effect that occurs when there is relative motion between a wave source and an observer.
What occurs because of the doppler effect?
The effect causes observed frequencies to be different than those actually emitted by the source, if the source is moving away then the frequency reduces, if the source comes closer then the frequency increases.
How to draw a Ray diagram for reflection in plane mirrors
Draw object and eye or observer, then draw your straight plane mirror line and label, draw the rays from the object to the observer, making sure to obey the law of reflection. Then draw dotted lines from where the rays hit the boundaries past the normals to the image (where the dotted lines intersect)
What properties does the image in a plane mirror have?
• Virtual(cannot be touched or projected)
• Upright (stand up in front of your mirror, you look the right way up)
• Latterally inverted (left side seems to be on the right in reflection)
How are sound waves made and why is a medium required?
Sound is made when an object vibrates and creates a longitudinal wave(pressure wave). This pressure causes particles in the surrounding medium to have vibrational motion, transmitting the sound further through the medium. Without a medium This pressure wouldn’t dissipate and no wave could form.
How does amplitude and frequency affect the sound?
Greater amplitude means that the sound gets louder, greater frequency means the pitch of the sound increases.
What does reflection of sound waves create.
Echoes.
What is the range of human hearing?
20Hz - 20kHz
What is ultrasound?
Ultrasound is sound with frequencies higher than 20kHz, since other animals have higher hearing ranges, animals like dogs can hear ultrasound whistles.
Uses of ultasound
• Breaking kidney stones
• Cleaning jewellery
• Foetal scanning
• Detecting cracks in machinery
How does sonar and medical ultrasound work?
Relies on when ultrasound waves meet at boundaries. Due to some waves being reflected, the doctors measure the time taken for a wave to leave and return and then from this create a depth boundary and hence a picture of inside.
What is the nature and properties of electromagnetic waves
Electromagnetic waves are transverse waves and travel at the speed of light in a vacuum
What are the component parts of the spectrum?
Gamma, X-rays, Ultraviolet, Visible light, Infrared, microwaves, radio waves
In order of increasing wavelength, what is the spectrum?
GXULIMR
In order of increasing frequency, what is the spectrum?
RMILUXG
Applications and hazards of radio and microwaves?
Radio waves used for communication purposes such as TV and radio, no damage to humans.
Microwaves are used for cooking food and satellite communication, high f microwaves can be absorbed by food easily, increasing internal energy
Applications and hazards of infrared and visible light
Infrared waves used by electrical heaters, cookers and cameras which detect people in the dark, no effect apart from heating.
Visible light is what we see, used in fibre optics.
Applications and hazards of Ultraviolet, X-rays and gamma waves
All of these are ionising radiation and can increase risk of cancer.
UV - can kill bacteria in water and is good for the skin to produce vitamin D, too much is bad however.
X-rays can kill cancer cells and be used to take pictures of bone
Gamma rays can also kill cancer cells and be used in medical tracers.
What do the terms atomic number and mass number mean?
Atomic number - proton number
Mass number - Value of the mass
What is an isotope
Isotopes are elements with the same atomic number and number of electrons, but with varying neutron numbers.
What is a nuclide and what is the notation?
A nuclide is a nucleus of an element with a set atomic number and nucelon number showing, the nucleon number on top of the element with the atomic number below it
What is ionisation caused by?
The gaining/loss of electrons
Why do radioactive emissions arise?
They arise from unstable nuclei
Why do radioactive emissions arise?
They arise from unstable nuclei
How do emissions occur?
Randomly and can only be valued by probability and half life
Difference between alpha beta and gamma
Alpha - helium nucleus is emitted from nucleus
Beta - emittion of e‐ due to neutron forming proton and an electron
Gamma - electromagnetic radiation (energy)
What is a nuclear equation?
²¹⁹Rn86 ==> ²¹⁵Po84 + ⁴He2
¹⁴C6 ==> ¹⁴N7 + ⁰e-1
What are the relative penetrative abilities of alpha, beta and gamma radiation
Beta radiation is more penetrating than alpha, it can pass through skin but is absorbed by a few cm of body tissue or mm of aluminium.
Gamma radiation is the most penetrating of the three and is only stopped by lead, it can easily penetrate body tissue.
Alpha cannot pass through paper
What are the relative ionising abilities of alpha, beta and gamma radiation.
Alpha is the most ionising, followed by beta radiation and then gamma is the least ionising
What happens to alpha beta and gamma when place in electric/magnetic fields?
Alpha is +vly charged and beta is -vly charged whilst gamma is neutral. Due to this, alpha goes towards the -ve plate, bets goes towards the +ve plate and gamma has no effect. In a magnetic field, alpha and beta are deflected and gamma is unchanged
What is background radiation and why does it occur
Background radiation is the radiation that occurs naturally in our day to day life, natural reasons for this includes cosmic rays, rocks and soil and living things. Artificial reasons are also prominent in increasing background radiation from things like X-rays, nuclear weapons and nuclear power.
What are the dangers of ionising radiation?
Can damage DNA in cells and lead to cancer, alpha is most dangerous inside the body whilst beta and gamma are outside the body.
What are the uses of ionising radiation?
Radioactive tracers to trace inside the body (need short half life + not poisonous), radiotherapy, carbon dating, dating rocks, smoke alarms.
What is the definition for half life?
Half life is the time taken for a sample to decay by a half (of its unstable atomic nuclei)
Equation for power, force and velocity?
Power = Force x Velocity
What is impulse equation?
Force × change in time
What equation links power and rate of doing work?
Power = rate of work = rate of energy transfer = change in power / time
K = Force/ extension
What is the toungs modulus?
Stress / strain
What is the equation for stress?
Force / cross sectional area
What is the equation for strain?
Extension / unstressed length
What represents strain energy?
Are under force - extension graph or strain energy = 1/2Fx = 1/2kx²
Which is at the open end of a tube? A node or antinode?
An antinode
What is the equation for the refractive index?
n = v1 / v2 = sin(angle)1 / sin(angle)2
Another equation for index?
n = 1 / SinC
What is the equation with refractive index and critical angle?
N = 1 / sinC
Equation with power and voltage in?
P = V² / R
Equation for resistivity?
Resistivity = resistance × (cross sectional area/ length)
Potential divider circuit equations?
Vout / Vin = R1 / R1 + R2 and V1 / V2 = R1 / R2
