Physics year 1

The thing i always forget to include on wave diagrams

Partial reflection rays

speed of light in another substance equation

speed of light in vacuum/refractive index = speed of light

What does the refractive index show

How much slower that light moves in a substance compared to when its in a vacuum

How do wave properties change when it enters a substance of higher refractive index

Bends towards the normal, and wavelength and speed decrease while frequency remains constant

Conditions for total internal reflection

The medium change is from higher to lower refractive

The angle of incidence is greater than the critical angle

Why do diamonds sparkle

The critical angle is very small, so there is a higher probability that light rays are reflected many times before they emerge so the colours will be more spread out

What is the phenomenon that allows fibre optics to work

Total internal reflection

What layers are there in optical fibres

Core, cladding and sheath

What could happen when 2 fibres touch each othee

Crosstalk (loss of signal into another wire)

Why do we use digital signals instead of analogue

When analogue signals pick up noise (superpose with other waves) it is hard to tell where the peaks and troughs are meant to be

What is latency

How quickly a signal reaches its destination

What is bit rate

How much data is sent per second

What must we do to signal to have a high bit rate

Pulses must be quick and close together

What is a potential issue with high bit rate

Multipath dispersion can render the signal undetectable if all the peaks overlap

What does the sheath do

Prevent scratching to core, prevents crossover and add structural integrity

How can a scratch cause signal loss

Light refracts the wrong way due to changed shape

What does the cladding do (5)

Has a lower refractive index so light totally internally reflects in core

Prevents scratching of core

Reduces mobile dispersion

Increase signal strength

Prevent crossover

Attentuation meaning

Decrease in signal strength as it is absorbed by mediums down the wire

How do we prevent attenuation

Use red or infrared as light doesnt absorb those wavelengths

Signal boosters

Material/chromatic dispersion

Pulse widening due to using different wavelengths of light, which travel different speeds in glass

Modal dispersion meaning

Pulse widening due to path difference in optics

How can we reduce modal dispersion

Reducing the diameter of the core or by reducing it enough for single path dispersion

What is the difference between step index and graded index

Graded index changes the refractive index gradually so it bends back toward the centre more often

How can we prevent modal dispersion

Reducing diameter enough so it is a single mode fibre

Wave defintion

Transfer of energy without the transfer of matter by means of oscillation

What can oscillate to form a wave

Matter or fields

What is the difference between longitudinal waves and transverse waves

Transverse waves oscillate perpendicular to energy transfer, and longitudinal oscillate parallel

Example of longitudinal waves

P-waves, sound

Example of transverse waves

S-waves, light, string

What are the parts of longitudinal waves

Rarefaction and compression

How are the two ways waves can be graphed

Displacement against time or distance

Definition of amplitude

Maximum displacement from rest value

Definition of time period

Time for 1 complete oscillation

Definition of frequency

How many waves pass a point in 1 second

What is superposition

When waves overlap, the resulting wave is the sum of the overlapping waves

What is phase difference

Angle between their wave cycles

Coherence definition

Constant phase difference and same frequency

What happens when 2 identical waves travel in opposite directions

A standing wave is formed with 2 * amplitude

What is path difference

The difference in the distances that 2 waves travel between 2 points

In a stationary wave, what is the phase difference

At an odd number of anti nodes away, out of phase, an even number of anti nodes away is in phase

What is polarisation

Restriction of the oscillation of a wave into 1 plane

Why can longitudinal waves not be polarised

Because they can only vibrate in one direction (can’t be restricted to a plane)

What direction of polarisation passes through a vertical polaroid

A vertical polarisation (opposite polarisations can’t get through the polaroid)

How much unpolarised light gets through a polaroid

The intensity halves

How do sunglasses use polarisation

They have a vertical polaroid, which halves the intensity of light from the sun, and eliminates the horizontally polarised light from reflections so it is easier to see

How do we consider polarised light with microwaves

An antennas oscillating electric field forms vertically polarised light so receiving antenna must be the same direction, A vertical metal grid between the source and receiver will block (horizontal polaroid)

What is an easy way to set up a standing wave

Reflecting a wave back on itself with a string

What are the frequencies of a standing wave called

Resonant frequencies or harmonics

How many nodes are there on the nth harmonic

n+1

What pattern does a tube with powder and a loudspeaker show

there are piles of powders equally spaced at the nodes

how does wavelength affect the amount of diffraction

Increasing wavelength increases the diffraction up until when wavelength is greater than the slit width

What are examples of wave behaviour

Interference, diffraction

Examples of particle behaviour

Mass, momentum, photoelectric effect

What determines if something acts like a particle or wave

When de broglie wavelength is larger than the particle, it acts like a wave

Single slit diffraction pattern

A single bright fringe of double usual width, then slits of much lower equal intensity equally spaced

How to set up double slits

Set up a laser in front of a single slit, with double slit behind it so the light hitting the slits has 0 path difference and coherent

Why are lasers helpful in double slit experiments

They provide a source of monochromatic coherent light, so patterns can be clearly seen

Uses of diffraction gratings

reading optical drives

Spectral analysis of stars

What is the path difference of the waves at the dark fringes

n/2 * lambda

What is the path difference at bright fringes

n * lambda

In double slit, why do dark fringes and bright fringes form

At bright fringes. the waves superpose and constructively interfere at bright fringes and destructively interfere at dark fringes

What does single slit diffraction interfere with

It interferes with the waves from different parts of the slit

Double slit interference pattern

All are equal width with a high intensity central maximum, fringes much closer together than single slit

Ways to produce monochromatic light (without laser)

Discharge lamps, filters of white light

How many maxima are produced when d/lambda = 3.2 in a diffraction grating

7 (central maxima and 2 sets of 3 maxima)

Why can’t we calculate fringe spacing for diffraction grating

Because the fringes arent equally spaced

Why are there large areas of dark in diffraction gratings

Because at these positions all the different waves superpose and cancel each other out, it is lots of waves to constructively interfere

Double/single slit pattern with white light

A central white maxima, with fringes showing the colour spectrum from red closest to the outside and violet on the inside, with the spectra becoming wider further from the central maxima, shrinking the dark fringes

Diffraction grating with white light

Central white maxima, with spectra with violet on inside and red on outside where maxima would be. Maxima increase in width with increasing order.

Minimum Photon Frequency for Electron Liberation

The photon's energy, determined by its frequency, must be greater than the work function (energy needed to break bonds holding the electron) in order for an electron to be emitted.

What happens if a photon has a frequency higher than the threshold frequency?

The electron will be liberated, and the remaining energy becomes the kinetic energy of the electron.

Effect of Increasing Light Intensity when Photoelectric Emission Does NOT Occur

Increasing light intensity has no effect because each photon still carries the same amount of energy, which is not enough to liberate an electron.

Work Function

The energy required by an electron to overcome the metallic bond holding it in the metal.

Electron Volt

The kinetic energy of an electron that has been accelerated from rest through a potential difference of 1V.

How a Fluorescent Tube Works

High voltage applied across mercury vapor accelerates fast-moving free electrons, which collide with the mercury atoms, exciting them. Mercury electrons return to the ground state, releasing a UV photon. The tube's phosphorus coating absorbs the UV photons, and its electrons are excited, they cascade down the energy levels and emit visible light photons.

Evidence for Discrete Energy Levels in Atoms

Line emission and absorption spectra, as the lines appear at discrete points which show where a light photon of specific frequency and wavelength has been absorbed or emitted, this shows electrons can only absorb an exact amount of energy to be excited to the next discrete energy level.

Wave-Particle Duality

All particles have both particle and wave properties. Waves can have particle properties, e.g., light acts as a particle in the photoelectric effect and as a wave when it is diffracted.

Feynman diagram for electron capture

(Theres 2)

Feynman diagram for beta minus decay

Feynman diagram for beta plus

Feynman diagram for decay of a down quark

Exchange particle definition

A virtual particle that gives rise to forces between 2 other particles by transferring momentum/energy

Ionisation definition

An atom losing or gaining electrons

Isotope definition

The same number of protons but different number of neutrons in atom

Stable baryon

Proton

Anti kaon neutral

Anti down and strange

Kaon neutral composition

Anti strange and down

Possible quarks in pion neutral

Up and anti up or down and anti down

What do kirchoffs law state

The charge (current) into a junction must be the same as the charge out of said junction

The sum of the voltage of 1 loop is equal to 0

What is emf

Electromotive force, energy gained by unit charge (by a cell)

Resistivity is a physical property of a metal

How to find resistivity experimentally

Change the length of test wire and measure the new resistance, plot gradient if resistance-length graph and multiply by area of wire

What is a superconductor

A material which tends to 0 resistance at low temperatures/pressure

What are superconductors used for

MRI scans, trains, reducing energy lost in national grid

Frequency and voltage of mains

50Hz 230V

What is a rheostat

A variable resistor

Brightness of a bulb depends on what

Power

What is ohms law

The current between 2 points is directly proportional to the potential difference across the 2 points at a constant temperature