3.1 - Longitudinal & Transverse Waves : Waves

Question 1

What is a progressive wave?

Answer 1

A wave that transfers energy from one point to another without transferring the medium itself.

Question 2

What is the displacement of a wave? (x)

Answer 2

The distance of a point on the wave from its equilibrium position.

Question 3

What is the amplitude of a wave? (A)

Answer 3

The maximum displacement of a particle in the wave from its equilibrium position.

Question 4

What is the wavelength of a wave? (λ)

Answer 4

The distance between points on successive oscillations of the wave that are in phase. (a full oscillation).

Question 5

what is time period? (T)

Answer 5

The time taken for one complete oscillation or cycle of the wave. (Time for one wavelength to pass a point).

Question 6

What is frequency?

Answer 6

The number of complete oscillations per unit time. (Hz)

Question 7

What is the frequency-period equation?

Answer 7

f = 1/T (Frequency = 1/ Time period)
(Also written as T = 1/f)

Question 8

What is the speed of a wave equation?

Answer 8

c = fλ
Speed of a wave = frequency x wavelength

Question 9

What does the speed of a wave equation show?

Answer 9

• As the wavelength increases, the frequency decreases
• As the wavelength decreases, the frequency increases

Question 10

What does a longitudinal wave do?

Answer 10

Particles in the medium oscillate parallel to the direction of the wave’s propagation (travel).

Question 11

What does a transverse wave do?

Answer 11

Particles in the medium oscillate perpendicular to the wave’s propagation (travel).

Question 12

What is phase difference?

Answer 12

A measure of how much a point or a wave is in front or behind another.

Question 13

How can you tell if waves are in phase?

Answer 13

The crests or troughs are aligned.

Question 14

How can you tell if waves are antiphase?

Answer 14

When the crest of one wave aligns with the trough of another.

Question 15

How can phase difference be described with degrees/radians?

Answer 15

In phase = 360° or 2π radians
In anti-phase = 180° or π radians

Question 16

Example - calculate the ‘lag’ between the waves if there is a phase difference of 1/4λ.

Answer 16

1/4λ x 360 = 90° or
1/4λ x 2π = π/2

Question 17

What are 3 examples of transverse waves?

Answer 17

• Electromagnetic waves (like: radio, visible light and UV)
• Vibrations on a guitar string
• Seismic (S) waves

Question 18

What are 3 examples of longitudinal waves?

Answer 18

• Sound waves
• Ultrasound waves
• Seismic (P) waves

Question 19

What is a rarefaction?

Answer 19

A region in a longitudinal wave where the particles are furthest apart.

Question 20

What is a compression?

Answer 20

A region in a longitudinal wave where the particles are closest together.

Question 21

What type of wave can be polarised?

Answer 21

Transverse waves.

Question 22

What is the wavelength on a longitudinal wave?

Answer 22

Distance between 2 compressions or rarefactions.

Question 23

What is the wavelength on a transverse wave?

Answer 23

Distance between 2 peaks or troughs.

Question 24

What is polorisation?

Answer 24

When particle oscillations occur in only one of the directions perpendicular to the direction of wave propagation.

Question 25

Why does polarisation only occur in transverse waves?

Answer 25

Because transverse waves oscillate in any plane perpendicular to the propagation direction.

Question 26

What happens when transverse waves are polarised?

Answer 26

• Vibrations are restricted to one direction
• These vibrations are still perpendicular to the direction of propagation / energy transfer

Question 27

What is the direction of propagation?

Answer 27

The direction of the wave’s travel.

Question 28

What happens when you vertically polarise a transverse wave?

Answer 28

The wave only oscillates in one direction.

Question 29

What happens when you have 2 polarising filters, one vertical and one horizontal? (filters are perpendicular to each other)

Answer 29

The first filter will polarise the light and the second filter will stop all waves passing through.

Question 30

Why do you have to line up transmitting and receiving television aerials?

Answer 30

TV signals are polarised by the orientation of the rods on the broadcasting aerial. You must line up the roads on the receiving and transmitting aerial to get a better signal.

Question 31

What is partial plane polarisation?

Answer 31

This means if the surface is horizontal, a proportion of the reflected light will oscillate more in the horizontal plane than the vertical plane.

Question 32

What is an example of partial plane polarisation?

Answer 32

When light is reflected from a reflective surface like the surface of water or a wet road.

Question 33

How do polaroid sunglasses reduce glare?

Answer 33

They contain vertically oriented polarising filters which block out any horizontally polarised light. Partial plane polarisation occurs on reflective surfaces and they oscillate more on the horizontal plane. This will reduce glare from reflective surfaces.