Waves

Question 1

How do longitudinal waves oscillate? Draw a diagram.

Answer 1

In the same direction as the direction in which the wave transfers energy.

Question 2

How do transverse waves oscillate? Draw a diagram.

Answer 2

Perpendicular to the direction in which energy is transferred by the wave.

Question 3

Give 3 examples of longitudinal waves.

Answer 3

Sound waves, ultrasound waves and seismic P waves.

Question 4

Give 3 examples of transverse waves.

Answer 4

EM waves Light (an EM wave in itself) Seismic P waves Water waves

Question 5

Which label represents the amplitude of the wave?

Answer 5

N

Question 6

Which label represents the wavelength of the wave?

Answer 6

V, F

Question 7

Which label represents the time period of the wave?

Answer 7

V, F

Question 8

What does T represent?

Answer 8

A crest

Question 9

What does E represent?

Answer 9

A trough

Question 10

Define amplitude

Answer 10

The maximum displacement of a wave above the equilibrium (the maximum distance from the rest to the crest of a wave)

Question 11

What is amplitude measured in?

Answer 11

It depends on the type of wave (e.g. water wave = m, sound wave = Pa)

Question 12

Define wavelength (λ)

Answer 12

The distance between one crest and the next

Question 13

What is wavelength measured in?

Answer 13

m (metres)

Question 14

Define time period (T)

Answer 14

The time take for one complete wave cycle to pass a given point

Question 15

What is time period measured in?

Answer 15

s (seconds)

Question 16

Define frequency

Answer 16

The number of complete wave cycles that pass a given point per unit time/per second

Question 17

What is frequency measured in?

Answer 17

Hz (hertz)

Question 18

What is the relationship between frequency and time period?

Answer 18

f = 1 / T

(frequency (Hz) = 1 / time period (s))

Question 19

What is the relationship between wave speed, frequency and wavelength?

Answer 19

v = fλ

(wave speed (m/s) = frequency (Hz) x wavelength (m))

Question 20

Which 2 properties do all waves have in common?

Answer 20

They can all be refracted and reflected

Question 21

What is a wave?

Answer 21

A oscillating disturbance which transfers energy and information without transferring matter.

Question 22

What is another name for an oscillation?

Answer 22

A vibration

Question 23

Define a rarefaction.

Answer 23

A reduction in the density of a wave.

For example: a sound wave moving through air is made up of alternating areas of higher and lower density. The areas of lower density are called rarefactions.

Question 24

What is the speed at which all EM waves travel? What do we call this speed?

Answer 24

3 x 10^8 m/s

300 000 000 m/s

This is the ‘speed of light’.

Question 25

What is this effect known as?

Answer 25

The Doppler Effect

Question 26

What is the Doppler Effect?

Answer 26

The observed change in frequency and wavelength of a wave when its source is moving relative to an observer.

Question 27

Give 6 properties which all EM waves possess.

Answer 27

They all…

can be reflected

can be refracted

travel at the speed of light

all transverse waves

all transfer energy and information without transferring matter

can all travel through a vacuum

Question 28

Why does the Doppler Effect occur?

Answer 28

The speed of a wave is constant, therefore when the speed of the source increases, it ‘catches up’ to the wavefronts ahead, causing them to bunch up, and moves away from those behind, causing them to spread out.

Question 29

An ambulance is moving towards a girl standing by the side of a road. As it gets closer, she notices that the pitch of the sound seems to change. What is this change? Why?

Answer 29

She notices that the pitch of the sound seems to increase.

This is because pitch is the sensation of frequency, and the frequency appears to increase due to the Doppler effect: the wavelength of the wave appears to decrease as it moves towards her. Since f = v/λ, and the speed of the wave remains constant, the frequency must increase.

Question 30

An ambulance is moving away from a boy standing by the side of a road. As it gets further away, he notices that the pitch of the sound seems to change. What is this change? Why?

Answer 30

He notices that the pitch of the sound seems to decrease.

This is because pitch is the sensation of frequency, and the frequency appears to decrease due to the Doppler effect: the wavelength of the wave appears to increase as it moves away from him. Since f = v/λ, and the speed of the wave remains constant, the frequency must decrease.

Question 31

Draw a graph of how perceived frequency varies as the source of a sound moves towards, passes, then moves away from an observer.

Answer 31

Question 32

Define a wavefront.

Draw a diagram to illustrate your answer.

Answer 32

An imaginary plane which connects adjacent points on waves which are moving in phase (oscillating together), and is repeated every wavelength.