Waves

Question 1

Displacement

Answer 1

The distance and direction of a particle from the equilibrium position

Question 2

Amplitude

Answer 2

The maximum displacement of the particle from its equilibrium position.

Question 3

Wavelength

Answer 3

The distance between 2 successive points on a wave which are in phase with one another.

Question 4

Period

Answer 4

The time taken for a particle on the wave to complete one oscillation

Question 5

Frequency of a wave

Answer 5

The number of complete oscillations that pass through a given point in 1 second. Units: Hertz(Hz) or s⁻¹

Question 6

Phase and Phase Difference

Answer 6

Phase - A measurement of the position of a certain point along the wave.
Phase difference -Measured in degrees or radians, the amount by which one wave lags behind another wave.

Question 7

Path Difference

Answer 7

Measured in metres, the difference in the lengths of two waves

Question 8

Wave speed

Answer 8

Distance travelled by a wave each second

Question 9

Transverse waves

Answer 9

Waves whose oscillations are perpendicular to the direction of energy transfer e.g. electromagnetic waves

Question 10

Longitudinal waves

Answer 10

Waves whose oscillations are parallel to the direction of energy transfer. They consist of compressions and rarefactions e.g. sound waves
A compression is a region where particles are close to one another. (High pressure)
A rarefaction is a region where the particles are further apart. (Low pressure)

Question 11

What can be polarised?

Answer 11

Only transverse waves can be polarised.
Polarisation can be used in things such as polaroid sunglasses to reduce glare or in a camera to enhance the image.
TV and radio signals are polarised by the direction of the rods on the transmitting aerial. To receive these signals well, you must ensure the receiving aerial and the waves are in
the same plane.

Question 12

What is required for TIR to occur

Answer 12

The light must travel from a more optically dense to a less optically dense medium.
The angle of incidence of the light ray must exceed the critical angle of the interface.

Question 13

Intensity of a wave

Answer 13

The rate of transfer of energy per unit area perpendicular to the direction of travel of the wave

Question 14

Diffraction

Answer 14

A wave will spread out as it goes through a narrow gap or past an obstacle

Question 15

Principle Of Superposition

Answer 15

The Principle Of Superposition states that when two waves of the same kind meet at a point in space, the resultant displacement at that point is the vector sum of the displacements that the two waves would separately produce at that point

Question 16

Interference

Answer 16

Interference refers to the superposing of two or more coherent waves to produce regions of maxima and minima in space, according to the principle of superposition.

Question 17

Coherent

Answer 17

Two sources are coherent if they have the same wavelength and frequency and a fixed phase difference between them.

Question 18

Constructive interference and destructive interference

Answer 18

Constructive interference nλ
Destructive interference (n+1/2)λ

Question 19

Stationary wave

Answer 19

A stationary wave is the superposition of two progressive waves with the same frequency but moving in different direction.

Question 20

Describe how standing waves are created (6 marks)

Answer 20

Something causes vibrations
Wave propagates, transverse on a string/longitudinal in air
Wave is reflected
Initial wave and reflected wave are coherent, they have the same frequency and wavelength but travel in opposite directions
Reflected wave superpose with initial wave, alternating between constructive and destructive interference
Creates nodes and antinodes
Nodes are where wave is stationary and antinodes are where the wave vibrates the most.

Question 21

Describe and explain the pattern caused by white light (5 marks)

Answer 21

Central maximum is white because all colours have a maximum there, so we see the combination of white.
Edge of central maximum is red because red has the longest wavelength of the colours and therefore has the widest pattern
Other maxima look like a spectrum, with violet closest to the central maximum and red furthest from the central maximum because all colours have different wavelengths so their higher order maxima occur at different locations.

Question 22

Dispersion causes pulse broadening
Modal dispersion
Material dispersion

Answer 22

Modal dispersion: Some rays take longer to get to the receiver based on the path they take.
Material dispersion: Different wavelengths travel at different speeds in the core, which means they get to the receiver at different times.