A2 Physics 2021 Flashcards
Angular displacement in circular motion formula
arc length/radius
Radian definition
The angle subtended at the centre of a circle by an arc of length equal to the radius of the circle.
Speed in circular motion formula
v = (2πr)/t
Angular velocity in circular motion formula
w = θ/t = (2π)/t
Acceleration in circular motion is always towards the ______ of the circle
centre
Centripetal acceleration formula
a=v^2/r
Centripetal force formula
F=mv^2/r or F=mw^2r
A vehicle will not skid on a curved road if _______
Fcentripetal < Ffriction
What is an oscillation
The motion in which an object repeats the same movement in a regular cycle.
Angular frequency of an oscillation formula
w=2πf
Amplitude definition
Maximum displacement from equilibrium position.
Free oscillation definition
An object or system oscillating at it’s natural frequency with no external force applied other than the impulse that initiated the motion.
What is a restoring force
A force acting to push the object back to equilibrium position. Frestoring ∝ displacement
Acceleration in Simple harmonic motion formula
a=w^2r
What is a forced oscillation
When an oscillating object or system is driven by a periodic external force.
What is phase difference
The angle at which waves are out of phase - measured in radians
What is the derivative of sin
cos
What is the derivative of cos
-sin
Formula for speed at any point in an oscillation
v=w√x0 -x^2
Where x0 = amplitude
and x = displacement
Kinetic energy in SHM formula
Ek=1/2m^2A^2
Where A = amplitude
Maximum potential energy in a spring oscillation formula
Ep=1/2KA^2
Where A= amplitude
What is damping
A reduction in the amplitude of an oscillation as a result of energy lost from a system to overcome resistive forces acting in the opposite direction.
What is critical damping
When a system returns to equilibrium in the shortest possible time without crossing it due to a large damping force
What is light damping
When the resistive forces are light so the system passes through the equilibrium while decreasing amplitude.
What is heavy damping
When resistive forces are large. System returns to equilibrium slowly without crossing it.
What is natural frequency
When an oscillating system starts oscillating on its own at a frequency.
What is a driving/forced frequency
When a system oscillates from an external excitation with a frequency.
Resonance definition
An increase in amplitude that occurs when an oscillating system is forced to oscillate at it’s own natural frequency.
Occurs when Fnatural=Fdriving
What are some uses of resonance
Radio recievers, guitars
Sound intensity definition
The power delivered per unit area of a surface that is perpendicular to the direction of travel of the wave.
Intensity of a sound formula
I=Power/Area
NB: I∝1/r^2
How is ultrasound used in medical imaging
A high frequency (for high res) pulse is sent into the body and the echo is read as electrical signals to measure distance travelled.
What are 4 things that can be done to ultrasound waves
They can be: Reflected Refracted Scattered Absorbed
Acoustic energy definition
The disturbance of energy which passes through matter in the form of a wave
Acoustic impedance definition
A physical property which describes how much resistance an ultrasound pulse encounters as it passes through tissue
What is attenuation
The reduction of amplitude of a signal, electric current, or other oscillation.
What is a transducer
A device which produces ultrasound pulses- converts energy from 1 form to another.
What is a piezoelectric transducer
Introduces the ability to transmit high frequency ultrasound waves. Comprised of crystals such as quartz.
Acoustic impedance formula
Z = ρv
Transmitted intensity of ultrasound pulse equation
I = I₀ x e^-μx
Conservation of ultrasound intensity formula
I = Ir + It
Intensity reflection coefficient formula
α = (Z2-Z1)^2/(Z2+Z1)^2
How are ultrasound waves turned into images?
- Reflected waves return to transducer, transformed into voltage pulses.
- Voltage pulses amplified and processed to give image s.
What is an A-Scan
Amplitude scan - single transducer used to measure tissue depths
What is a B-Scan
Brightness scan - uses an array of transducers, each measuring amplitudes at a different angle, and plots each returning signal as a pixel on screen.
What are fixed points
Reference points on a thermometer - determined by physical properties of common materials.
What is absolute zero
The point of minimum motion of particles making up a substance.
What is triple point
The temperature at which all three phases of a substance exist.
What can be deduced from the difference in temp of 2 objects?
The rate of transfer of thermal energy
What is the basic principle by which temperature is measured
By measuring physical changes in the thermometric properties of a substance.
Why will some thermometers not give the same temperature reading for substance
For some thermometers, change in temperature may not be linear with change in thermometric properties.
What are the advantages of a thermocouple over a thermistor
- wider temp range
- linear scale
What are the advantages of a thermistor over a thermocouple
- smaller
- doesn’t require reference liquid.
- can be used remotely more easily
What is the ideal gas equation
PV = nRT
What are the 5 assumptions of the kinetic theory of ideal gas.
- Collisions of particles are completely elastic
- There are no external forces between molecukes
- Molecules move with constant velocity
- Total volume of molecules is much less than total volume of the gas
- Motion of the molecules is completely random
Heat definition
Total energy of all molecular motion inside an object
Temperature definition
Average kinetic energy of particles within a substance.
Specific heat capacity formula
Q=mcΔt
Specific latent heat formula
Q=mL
Why is latent heat of vaporization higher than latent heat of fusion?
Energy required to completely separate molecules is much greater than slightly seperate them.
What is internal energy
The sum of all Ek and Ep in a system.
What is the first law of thermodynamics
The total energy in an isolated system is constant
Internal energy formula
ΔU = Q + W
Work done on a contained gas formula
W = PΔV
What are the 2 types of capacitor
- Isolated
- Parallel plates
Capacitance definition
The ability of an electric system to collect and store energy in the form of electrical charge.
Capacitance formula
c = Q/V
Capacitance unit
Farad, F
Energy store in electric field formula
E=1/2QxV (are under graph)
Capacitance of air filled capacitor formula
c=ε₀x(A/D)
Capacitance of dielectric filled capacitor formula
c=ε₀εᵣx(A/D)
How will a potential difference be applied between plates of a capacitor
- Electrons at plate A will have more electrical potential energy causing electrons to move to plate B.
- This will cause a deficit of electrons at plate A and a surplus of electrons at plate B.
- This creates an electric field between the two plates in the direction of positive to negative. (E=V/D)
Work done between parallel plates formula
W=QV
Electrical potential energy formula
Ep=QV
What is the net charge in the centre of a capacitor
Zero
How is energy stored in a capacitor
In an electric field in the form of charges
2 uses of capacitors
- Storing energy
- Blocking D.C. in circuits
Charging a capacitor formula
Q=It
Time taken to charge a capacitor formula
T=RC
R=Resistance
C=Capacitance
3 applications of op-amp
- Acting as a switch when voltage reaches certain level
- Amplifying voltage and current signals
- Voltage comparator
Formula for Vout of op-amp
Vout = A₀(V+ - V-)
Formula for A gain of op amp
A₀=Vout/Vin = Vout/(V+ - V-)
What is the typical value for A₀
1x10^5
What are voltage supply rails for
They will saturate the voltage output
What is slew rate
The time delay between the rate of change between input voltage and output voltage.
What is Vcc
Common collector voltage - supplies equal voltage to all nodes connected to it
Potential divider formula
Vout = Vin(R2/R1+R2)
An LED works in forward bias - this means?
When the potential at the anode is greater than at the cathode it turns on.
As light intensity increases, resistivity of LDR _____
Decreases
As temperature increases, resistivity of thermistor ______
Decreases
Resistance of wire formula
R=ρL/A
What is a metal strain gauge
Device used to measure strain/stress of a material of a structure
Symbol for resistivity
ρ
What is feedback
A process in which a fraction, β of the amplifier output is added back to the input. This is called the feedback fraction.
What is negative feedback
When a negative fraction, β of the output is sent back into the inverting terminal (V-)
Formula for Vout with feedback
Vout = A₀ x (Vin - βVout)
3 benefits of using negative feedback
- Increases bandwidth
- Reduces distortion
- Prevents saturation
What is virtual ground
- A fraction of the output is connected to the input, making Vout virtually 0V.
- The input becomes smaller such that V+ is approx. equal to V-
- The assumption that Vin = 0 is called virtual ground.
What is a non-inverting op-amp
When Vin goes into the non inverting terminal (V+)
What is a relay and how does it work
Electromagnetic switch that can open and close circuits. When the coil is switched on, it creates an electromagnetic field which pulls a switch shut.
Define magnetic field
A region around a magnetic material or moving electric charge within which a magnetic force acts.
What points to current and field direction in right hand grip rule
Thumb - current direction
Fingers - Magnetic field direction
What points to current and field direction of SOLENOID in right hand grip rule
Thumb points north
Fingers in direction of current
3 ways to increase magnetic field strength in a coil
- Increase current
- Shorten the coil
- Increase turns in coil
Which fingers point where flemings left hand rule
Thumb - Force
First finger - Magnetic field direction
Second finger - Current direction
Magnetic force on a conductor formula
F=BIL
Magnetic force on a conductor at an angle formula
F=BILsinθ
What is magnetic flux density
The strength of the magnetic field
Formula for magnetic flux
Φ=BAcosθ
Formula for magnetic field strength along a straight wire
B = (µo x I) / (2πd)
The magnetic field due to a straight wire is ______ proportional to the distance from the wire
inversely
Formula for force between two parallel wires
F = (µo x I1 x I2 x L) / (2πd)
Unit for magnetic field strength
T, Tesla
Formula for magnetic flux density along a solenoid
B = µo x n x I
Formula for magnetic flux density inside a flat coil
B = (µo x I) / (2πd)
Formula for torque along a moving coil
τ = NIABsinθ
Formula for force on a moving charge in a magnetic field
F = BQv
Formula for drift velocity
I = nQvA
Formula for hall voltage
V = BI / net
How is hall voltage created
- Hall voltage is the potential difference across a semiconductive material.
- Electrons are passed into the material and due to the electric current, they experience a force causing the semiconductor to have a positive and negative side.
- However electrons are then attracted to the positive side creating a net 0 charge.
Two ways to measure force created by circuit
- Current balance
- Hall probe
Formula for radius of circular motion of a charge in a magnetic field.
Fc = Fb
Therefore: r = mv / BQ
Formula for specific charge
Q / m
How do MRI scans work
- Radio waves are sent into the body and the NMR causes hydrogen nuclei in the body to move around.
- When the radio waves are stopped, the hydrogen nuclei return to position and release radio waves as energy which can be detected.
When should X - ray be used
To see bone structures
When should MRI be used
To scan the brain and its tissue
Wehen should ultrasound be used
To measure depth of body structures
3 ways to increase induced voltage
- Increase speed of motion
- Increase number of turns in coil
- Increase strength
What finger points to what in right hand generator rule
Thumb - Force
First finger - Magnetic field direction
Second finger - Current direction
Formula for induced e.m.f
ℰ = NBLv
Formula for magnetic flux induced in a coil
Φ=BANcosθ
Formula for e.m.f across a conductor
ℰ = BLv
Formula for e.m.f of a conductor of N coils
ℰ = -NΔΦ / Δt
What is Lenz’s Law
When an e.m.f is generated by a charge in magnetic flux, the polarity of the induced e.m.f produces a current that’s magnetic field opposes the force which produces it.
What is Faraday’s Law
When a charge is passed through magnetic flux it will generate an e.m.f
What are eddy currents
- Undesirable currents created when a current is induced in a conductor
- These spiraling currents are in the opposite direction to the induced current and cause power loss as heat
What is the formula for average Ek of a single gas molecule at a given temperature
Ek = 3/2Kt
Where k = boltzmann contstant
What are 3 differences between waves and particles
Wave: Has no mass, can pass through particles, can occupy same position causing interference.
Particle: Has a mass and cannot pass through other particles, cannot occupy same position.
How is electromagneticc radiation produced
- Atom absorbs energy
- Energy causes 1 or more electrons to change their locale within the atom
- When the electron returns to its original position, EM radiation is produced.
How is electromagnetic radiation propagated through a medium
In the form of EM waves.
What is light in the form of.
A pocket of energy which can behave as waves and particles.
What is a quantum
A discrete quantity of energy proportional in magnitude to the frequency of its radiation.
What is a photon
A particle representing a quantum of light or other EM radiation
What is photon energy
The energy carried by a single photon
Formula for energy of a photon
E = hf , E=hc/λ
What does h stand for
Planck constant - 6.63x10^34J/s
Energy of a single photon is proportional to its _______
frequency
What instrument is used to demonstrate the photoelectric effect
Electroscope
What is the photoelectric effect
The process where light is used to free electrons from the surface of a metal.
What are the 5 steps in using an electroscope.
1) Light is shone through a quartz window
2) Cathode ejects electrons into vacuum
3) Electrons through vacuum to anode
4) Electrons move through wire from anode to cathode
5) Ammeter is used to measure the store of electrons.
What are 3 observations from phillip lenard experiment
Intensity of incident light had no effect on the maximum kinetic energy of the photo electron.
Increased intensity does however result in increased rate in emission of electrons.
There is a minimum frequency required for electrons to be emitted called threshold frequency.
Formula for work function
Φ = hf0
Formula for maxiumum Ek of electron from a photon
Ekmax = hf/Φ
What is the work function
The minimum amount of energy required for an electron to escape the surface of the metal.
What does a diffraction grating prove
That particles can behave as waves.
What shape is the pattern formed when electrons are diffracted through a diffraction grating
ring shape
If electrons are diffracted at high voltage, rings will be ______
Close together
If electrons are diffracted at low voltage, rings will be ______
Far apart
What is the de broglie wavelength
The wavelength formed between the rings of diffracted electrons.
Formula for de broglie wavelength
λ = h/p = h/mv
Formula for accelerating voltage of an electron through a grating
Ek = eV = 1/2mv^2
Formula for bragg’s law
nλ = 2dsinθ
How are spectrum lines formed
From emission and or absorption of light in a narrow frequency.
What is the definition of a hole
Empty vacancies for electrons to fill in.
What is the conduction band
The next outer shell from the valence shell which electrons can jump to when in an excited state. Electrons must be in the conduction band in order to be conductive.
What is the forbidden gap
The energy difference between valence and conduction bands which electrons must cross.
What is the fermi level
The forbidden gap
In an insulator, is the forbidden gap small or large
Large
How are holes formed.
When an electron jumps from the valence shell to the conduction band, a hole is left behind.
When heating a material, why does resistance initially increase?
Due to increase vibrations of the particles, it initially impedes the flow of electrons through the material.
Why are metals strong conductors? (Refer to shells)
Valence and conduction bands overlap. Therefore they’re always conductive.
How does an x-ray tube work
Electrons accelerated towards anode, which deflect off tungsten into x-ray window.
Why do intensity peaks occur in tungsten
When electrons are knocked off the surface off the tungsten
2 ways to increase intensity of x-rays
Use a higher potential difference
Use a higher energy
How do you make the resolution of an x-ray image higher
Make the surface area of the anode smaller
What is used to mitigate deflected radiation during x-ray
Lead grating
What is attenuation
The decrease in intensity of radiation as it enters a material
Formula for fraction of transmitted intensity of x-ray
I/Io = e^-µx
What is the symbol for the linear attenuation coefficient
µ
What is the formula for the linear attenuation coefficient
µ = no. of photons that interact / total no. of photons
What are 2 features of hard x-rays
Shorter wavelength, higher energy
What are 2 features of soft x-rays
Longer wavelength, lower energy
What is half value thickness
The thickness of a material that reduces the intensity of an x-ray by 50%
In what ways are CT scans better than x-ray
More detailed images, 3D images.
Can also reveal soft tissue, organs.
What is a voxel.
A number representative of the rate of attenuation of a material.
5 stages of working out a voxel
1) Analyse the resultant attenuation
2) Pick a sample and double it
3) Pass each resultant scan through it
4) Subtract initial attenuation rate
5) Divide whole voxel by 3
What is 1u in kg
1.66x10^-27kg
Formula for conservation of energy
E = mc^2
What is mass defect
The difference between the actual mass of an atom and the sum of the masses of it’s constituents.
Why is there a mass defect
The energy which binds the constituents together is seem as mass when the atoms split up.
What is nuclear fission
Sending neutrons at high speeds into large nuclei, causing them to split into smaller nuclei and release energy
What is nuclear fusion
Speeding up small nuclei using very high temp and pressure to overcome the strong interaction and form a single nucleus.
In fission, binding energy per nucleon _______
decreases
In fusion, binding energy per nucleon _______
increases
What instrument is used to measure radioactivity
Geiger-muller counter
What is the symbol and unit for activity
Symbol: A
Unit: Bq (Bequerel)
What 2 things does activity depend on
- Amount of substance
- Half life of substance
Formula for activity
A = ΔN/Δt
Formula for activity at time t
A(t) = Ao x e^-λt
What is the formula for decay constant
λ = ln2 / half life
What is the definition of half life
The time taken for the no. of radioactive nuclei in/activity of a sample to halve
What is a spontaneous process
A process that cannot be sped up or slowed down by physical means.
What is a random process
Impossible to predict which nucleus and when it will decay
What is the formula for constant ratio
N1/N2 = e^-λ(t1-t2)
