Zusammenfassung der Ressource
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