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A Level Physics OCR

Molly Walker Physics A level English

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A Level Physics OCR

Imaging
- Lenses
  - Curvature of a circle = 1/r
  - Wave-fronts with a distant source appear to have no curvature
    - Plane wave-fronts
  - Rays travel in the direction of motion of the wave front
    - They are at right angles to the wave front
  - Power = 1/f
    - Dioptres (D)
- Finding The Image
  - 1/v=1/u+1/f
  - f is the point at which parallel waves are brought to focus
  - The image distance v is greater than f apart from very distant objects
  - Magnification
    - m = image height / object height
    - m = image distance / object distance
      - m = v / u
    - A negative m occurs when the image is inverted
- Storing and Manipulating the Image
  - Pixels store electric charge when light falls on it
    - The brighter the light, the greater the charge
  - Bits and Bytes
    - 8 bits = 1 byte
    - N = 2^b
    - b = log2(N)
  - Resolution
    - Object width / pixels across object
  - amount of information = number of pixels x bits per pixel
- Processing
  - Changing brightness
  - Removing noise
  - Edge detection
  - Changing contrast
- Polarisation
  - Speed = frequency x wavelength
  - Frequency = 1 / T
  - Transverse waves
    - They are polarised if they travel in one plane
    - Unpolarised waves vibrate randomly
Signalling
- Digitisation
  - Sampling occurs are small time intervals
  - Analogue Signals
    - Amplification of analogue signals amplifies the noise as well
    - Filtering noise lowers the level of detail in the signal.
  - The difference between the signal value and the quantisation level is a quantisation error.
  - Resolution
    - Potential difference range of signal / number of quantisation levels
  - Useful levels
    - Max useful number of levels = total noisy signal variation / noise variation
    - b = log2 (V total / V noise)
- Sampling and Sending
  - minimum sample rate > 2x highest frequency
  - The signal cannot contain frequencies above a maximum
    - If it is higher, aliases will be produced
      - Aliases are lower frequency signals not in the original signal
  - Bit rate = samples per seconds x bits per sample
  - Duration of signal = N of bits in signal / bit rate
Sensing
- Current, P.D, Power
  - Current
    - Flow of charged particles
      - Charge
        Q
        Coulombs C
    - Amperes/Amps A
    - I
    - Current = Charge / Time
    - Currents at a junction must add up
  - Potential Difference
    - Voltage V
      - P.D
    - Work done = Change in energy
    - V = E / Q = W / Q
  - Power
    - Watt W
    - P
    - Power = Current x voltage
  - Resistance
    - R = V / I
    - Ohms
      - VA^-1
    - P = I^2R
- Conductors and Resistors
  - Conductance
    - G = I / V
    - AV^-1
      - Siemen
    - G = 1 / R
    - The amount of amps from 1V
  - Resistance
    - The ratio of P.D to current
    - I is proportional to V
  - Parallel Circuits
    - 1/R1 +1/R2
    - Same P.D
    - Shared current
    - Conductances add
      - G = G1 + G2
  - Series
    - 1/G1 + 1/G2
    - Resistances add
      - R = R1 + R2
    - Same Current
    - Shared P.D
- Conductivity and Resistivity
  - Conductivity
    - G = OA/L
    - Sm^-1
  - Resistivity
    - Doubling the length doubles the resistance
    - R = PL/A
    - Ohmic metres
Materials
- Testing Materials
  - Classes
    - Hard - difficult to scratch
    - Tough - Difficult to break
    - Brittle - shatters into jagged pieces
    - Stiff - difficult to stretch and bend
    - Malleable - shaped easily
    - Ductile - can be drawn into a wire
  - Stretching Wires
    - Hooke's Law
      - F = kx
      - k is the spring constant
        k depends on the material, length and CSA
    - An elastically deformed wire can return to its original length
    - Exceeding the elastic limit causes plastic deformation
      - Fracture occurs after plastic deformation
    - E = 1/2 kx^2
  - The Young Modulus
    - Stress
      - Force per unit area
      - PA
      - Yield stress - point at which plastic deformation begins
      - Force / CSA
    - Strain
      - Extension / Length
        X / L
        %
      - Fractional increase in length
    - E = FL / xA
    - Often very large
- Looking Inside Materials
  - Rayner
    - Oil drop
    - h = 4r^3 / 3R^2
  - Number of atoms = total mass / mass of one atom
  - Metal Structure
    - Metals are crystaline
    - Dislocations
      - Mismatches in rows of atoms
      - Atoms move individually rather than as rows
      - Pinned dislocations (addition of an atom) make the slip harder
    - Glass is amorphous
    - Crack Propagation
      - Elastic straining occurs
      - Two atoms are pulled apart
      - It acts like a zip
  - Bonding
    - Metals
      - Metal bonds are strong, making them stiff
      - Ions are free to move - ductile and tough
    - Polymers
      - Bonds rotate, stretching the chain
      - The chain starts off folded
Wave Behaviour
- Superposition
  - If two waves are at the same point, they are in phase
  - Two waves doing the opposite are in anti-phase
  - Otherwise they are 'not in phase'
  - When two or more waves overlap
  - The sum of phasors gives the resultant amplitude
  - On a string
    - Waves move along a string
    - They reflect and superpose
    - Antinodes are where waves meet at a maximum amplitude in phase
    - Zero amplitude in antiphase creates nodes
- Velocity = wavelength x frequency
- Refraction
  - Refractive index = c in medium 1 / c in medium 2
  - RI of material = c vacuum / c material
  - Snell's Law
    - The ray bends towards the normal
    - sin 1 / sin r
    - c first / c second
- Diffraction
  - Young's Double Slit
    - Light passing through two small pinholes create bright and dark spots
    - Light going through a slit spreads out
    - When in phase, a bright fringe is created
    - Sin(angle) = wavelength / slit separation
  - Order of Maxima
    - The 0th order is where the path difference is 0
    - Wavelength = xd/L
    - Line separation = 1 / lines per m
Quantum Behaviour
- Packets of light are called quanta
- Quanta
  - EM radiation is emitted and absorbed in quanta
  - Energy = Planck constant x frequency
    - The Planck constant is 6.6 x 10^-34 Js
    - E = hc / wavelength
- The Photoelectric Effect
  - Intensity is the amount of energy transferred per metre squared per second
  - KE is not affected by intensity
  - If f is lower than the threshold frequency no elections are released regardless of how bright it is
  - Maximum energy depends on light frequency
  - EK(max) = hf - work function
    - The work function is the energy needed to release the electron from the surface
- Probability
  - Square the amplitude to find the chance
  - Add phasors tip to tail
- Reflection
  - Photons obey the law of refraction
  - Phasors from end paths curl up
- Electron Diffraction
  - Wavelength = h/mv
Motion
- Graphs
  - Displacement - distance travelled from the starting point
  - Velocity - the speed including direction
  - Avg v = s / t
  - A = v / t
- Modelling Motion
  - Iterative models
    - Step by step
    - It assumes a constant DV
    - Accuracy can be improved with smaller time intervals
      - Vectors can be used
  - SUVAT
    - v = u + at
    - s = (u + v) / t
    - s = ut + 1/2at^2
    - v^2 = u^2 + 2as
    - s = (u + v) / 2
- Momentum, Force, Energy
  - Momentum
    - p = mv
    - Total p = m1v1 + m2v2
    - Momentum is conserved
      - Momentum before equals the momentum after
  - Newton's laws
    - Momentum will not change unless a force acts upon it
    - F = p / t
      - F = mv /t
    - If a exerts a force on b, b exerts a force of equal magnitude and opposite direction on a
  - F = ma
  - Energy
    - Work = force x displacement
    - Kinetic Energy = 1/2mv^2
    - Gravitational potential = mgh
  - Work and Power
    - Work = Fs
      - Fs x cos(angle)
    - Power = work done / time
Modelling
- Decay
  - Decay and Half-Life
    - Types
      - Alpha - Helium nuclei
      - Beta - fast moving electrons
      - Gamma - high energy photons
    - Activity and Half-Life
      - Activity A
        1 Bq
        1 decays^1
        Number of nuclei decaying per second
      - Half- Life
        T1/2
        N is reduced by 2^L
        L half lives
      - Time required for the sample to half
      - A = prob of decay in 1s x N
    - A=A0e-^-λt
      - T1/2 = LN2/ λ
        - λ is the gradient
  - Capacitors
    - Electrical conductors separated by a layer of insulator
    - Capacitance
      - C=Q/V
      - Charge separated per volt
      - Farad F
        CV^-1
      - E=1/2QV
    - Q=Q0e^-t/RC
    - t=RC
      - RC is the time constant of discharge
- Oscillations
  - Simple Harmonic Motion
    - Time period is the time for once complete swing
    - The displacement is about an equilibrium position
    - x = Acosωt
      - ω = 2πfrad/s
    - Acceleration
      - Proportional to the displacement
      - Is always directed towards the equilibrium position
      - a = -kx
        a = -ω^2x
  - Time and Frequency
    - T = 2π√ m/k
    - Pendulum
      - F = -T x/L
      - a = -g x/L
      - T = 2π√L/g
  - Resonance
    - Free Oscillations
      - It will have a constant amplitude
      - It swings at a constant, natural frequency
        When the driving and natural frequency match, it goes into resonance
    - Forced Oscillations
      - A periodic driving force causes the driving/forced oscillation
      - e.g Marching soldiers on a bridge
    - E = 1/2 kA^2
      - E = Ek + Ep
  - Damping
    - The action of forces such as friction
    - Removal of energy from a system
- Gravitational Field
- The Universe
Matter
Fields
Particles

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Description: A level Physics Mind Map on A Level Physics OCR, created by Molly Walker on 22/04/2017.
Created by: Molly Walker
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