A Level Physics OCR

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

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A Level Physics OCR

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	Created by Molly Walker about 7 years ago