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8624605
A Level Physics OCR
Description
A level Physics Mind Map on A Level Physics OCR, created by Molly Walker on 22/04/2017.
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physics
a level
Mind Map by
Molly Walker
, updated more than 1 year ago
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Created by
Molly Walker
over 7 years ago
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Resource summary
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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