WJEC AS Physics - Unit 2.4, 2.5 + 2.6

Progressive wave

A pattern of disturbances travelling through a medium and carrying energy with it, involving the particles of the medium oscillating about their equilibrium positions

2 types of progressive waves

Transverse and Longitudinal

Transverse wave

A transverse wave is one where the particle oscillations are at right angles to the direction of travel (or propagation) of the wave

Longitudinal wave

A longitudinal wave is one where the particle oscillations are in line with (parallel to) the direction of travel (or propagation) of the wave

Polarised wave

A polarised wave is a transverse wave in which particle oscillations occur in only one of the directions at right angles to the direction of wave propagation

Examples of transverse waves

• Water waves

• Waves on a spring

• All EM waves

Examples of longitudinal waves

• Sound waves

• P-waves (seismic waves)

Displacement of a wave

Displacement is the shortest distance of a wave particle from its equilibrium position

Amplitude of a wave

Amplitude is the maximum displacement of a wave particle

Phase of a wave

If a particle along the wave is in phase with another, then it means that they are in the same point in the cycle at the same time. If they are at the opposite points in the cycle at the same time then they are called anti phase

Period of a wave

The time of one complete cycle. It is related to the frequency by the equation T=1/f. Where T=the period and f=the frequency

Speed of a wave

The distance that the wave profile moves per unit time

Equation for the speed of a wave

c=fλ

Wavelength of a progressive wave

The wavelength of a progressive wave is the minimum distance (measured along the direction of propagation) between two points on the wave oscillating in phase

Frequency of a wave

The frequency of a wave is the number of cycles of a wave that pass a given point in one second [or equivalently the number of cycles of oscillation per second performed by any particle in the medium through which the wave is passing]

How wavefronts can be produced

Using a ripple tank

What is always perpendicular to the wavefront

The direction of propagation

Distance between adjacent wave front is what

Wavelength

All the points on a wave front oscillate in what

Phase

The frequency of wave fronts

The frequency is the number of wave fronts that pass a point per second

Polarisation

The effect of passing light though a polarising filter

How many planes of vibration will a polarisation filter allow to pass

One

What polarisation does to light

Cause it to become plane polarised

Wave type with which polarisation will only occur

Transverse

Result of placing two Polaroid filters so that their angles of polarisation are at 90 degrees to each other

No transmission of light

What cross polaroids are used in

Stress analysis using plastic structures as a model

What appears when a plastic model is placed between two filters as one is turned relative to the other

Coloured lines of stress

In phase

Waves arriving at a point are said to be in phase if they have the same frequency and are at the same point in their cycles at the same time.

Wave sources are in phase if the waves have the same frequency and are at the same point in their cycles at the same time, as they leave the sources

Diffraction

Diffraction is the spreading out of waves when they meet obstacles, such as the edges of a slit. Some of the wave’s energy travels into the geometrical shadows of the obstacles

Principle of superposition

The principle of superposition states that if waves from two sources [or travelling by different routes from the same source] occupy the same region then the total displacement at any one point is the vector sum of their individual displacements at that point

Constructive interference

When the same parts of two waves from coherent sources occupy the same space e.g. 2 troughs or 2 crests

Destructive interference

When opposite parts of two waves from coherent sources occupy the same space e.g. a trough and a crest

Interference pattern

When waves from two identical sources meet

Coherent sources

Sources where everything about the sources are identical

How an interference pattern is produced

Alternate lines of constructive and destructive interference

Because the sources in an interference pattern are identical, what are the lines of constructive and destructive interference?

Fixed

If the sources of an interference pattern is light, how could it be displayed on screen?

Alternating dark and bright fringes

What is used to show interference

2 coherent sources of light

What the Young’s double slit experiment show

• light has a wave nature

• Allows for the measurement of wavelengths of light

Equation for Young’s double slit experiment

Rearrangement of equation for Young’s double slit experiment

Assumptions that Young’s double slit experiment equation relies on

D > a

change in y > a

Path difference at O in Young’s double slit experiment is given by

Meaning of path difference being given by S2O-S1O=0

Must be whole number of what for a bright band to appear at P

In Young’s double slit experiment, for a bright band to appear at P there must also be a whole number of wavelengths difference between S2P and S1P. This causes what equation to be true?

Path difference at O for a dark band to appear

For a dark band to appear then the path difference at O must be half a wavelength difference. This causes what equation to be true?

Diffraction effect if λ < d

Diffraction effect if λ =d or λ > d

Diffraction effect if λ > d

Advantages diffraction has over an interference pattern

What the advantages diffraction has over an interference pattern

Diffraction grating

Pattern produced if monochromatic light is incident on the plate of a diffraction grating

Diffraction grating works on same principle as what

Equation for diffraction gratings

Stationary wav

Nodes

Antinodes

Intermodal distance

Intermodal distance is equal to

Method for determining the speed of sound in air

1st position of resonance in determining the speed of sound of air

Equation for determining the speed of sound of air practical

Energy transfer properties in stationary waves

Energy transfer properties in progressive waves

Amplitude of stationary waves

Amplitude of progressive waves

Frequency of stationary waves

Frequency of progressive waves

Wavelength of stationary waves

Wavelength of progressive waves

Phase difference between 2 particles in stationary waves

Phase difference between 2 particles in progressive waves

Diagram for determining speed of sound in air

Phase difference

Coherence

Stationery wave

Refractive index

Snell’s Law

Critical angle

Refraction

Equation for refractive index

Diagram for Snell’s Law

Total Internal Reflection

Critical angle and total internal reflection

Conditions for total internal reflection

Fibre optics

Monomode fiber

Multimode fiber

Advantages of monomode fibres

Disadvantages of monomode fibres

Advantages of multimode fibres

Disadvantages of multimode fibres