Chapter 12 - Waves and vibrations

Question 1

What are transverse waves?

Answer 1

Vibrations that are perpendicular to the flow of energy.

Question 2

What is a progressive wave?

Answer 2

A wave which energy moves in one direction.

Question 3

How can you distinguish between longitudinal and transverse waves?

Answer 3

Transverse waves can be polarised but longitudinal can’t.

Question 4

What does polarisation mean?

Answer 4

To allow waves to vibrate in only one plane. Unpolarised waves change from one plane to another.

Question 5

Where would you find polarising filters?

Answer 5

Sunglasses to reduce glare.
3D cinema spectacles to see 3D movies.
Windscreens to reduce glare.

Question 6

Define the amplitude of a wave.

Answer 6

The maximum displacement of a particle from its equilibrium position.

Question 7

Define wavelength.

Answer 7

The maximum distance between two adjacent crests or particles with the same displacement and velocity.

Question 8

Define frequency.

Answer 8

Number of cycles of a wave in one second.

Question 9

What is superposition?

Answer 9

When two waves meet, the total displacement is the sum of the individual,displacements at that point.

Question 10

How is a stationary wave set up?

Answer 10

Waves with the same frequency and wavelength travelling in opposite directions form nodes (areas of no displacement) and antinodes (areas of maximum displacement). Nodes are the result of destructive interference and antinodes the result of constructive interference.

Question 11

What are coherent waves?

Answer 11

Waves with the same frequency and a constant phase difference. These are waves that form interference patterns when they overlap.

Question 12

What is monochromatic light?

Answer 12

Light containing only one wavelength.

Question 13

What is the difference between a progressive wave and a stationary wave?

Answer 13

There is no net transfer of energy in a stationary wave.

Question 14

What is a longitudinal wave?

Answer 14

The direction of vibrations is parallel to the flow of energy, composed of areas of compressions and rarefactions.

Question 15

Describe the vertical displacement of a particle in a transverse wave from the start of the cycle.

Answer 15

Moves vertically upwards to max displacement for a 1/4 cycle, then vertically downwards to equilibrium position, then vertically downwards to maximum negative displacement then finally vertically upwards for the last 1/4 cycle to equilibrium position.

Question 16

How would a particle in a wave become motionless?

Answer 16

A wave with the same frequency and amplitude moving in the opposite direction destructively interferes to form a node. A stationary wave forms. Waves cancel where the particle is. Node = no movement.

Question 17

What is an antinode?

Answer 17

Point of maximum disturbance on a stationary wave. This is caused by constructive interference of in phase waves.

Question 18

What is a node?

Answer 18

Two waves cancel due to 180degrees phase difference.

A point of minimum or no disturbance.

Question 19

Explain why it is important to correctly align an aerial of a TV in order to receive the strongest signal.

Answer 19

Radio waves are often polarised. Aerials must be aligned in the same plane of the wave.

Question 20

If a seismic wave is polarised what does it tell you about the wave?

Answer 20

It is a transverse wave as longitudinal waves can’t be polarised. The oscillations of this wave are in one plane.
Seismic waves can be transverse or longitudinal.

Question 21

How can a player of a stringed instrument increase the fundamental frequency of a note?

Answer 21

Decrease the length of the string
Increase the tension of the string
Tighten the string

Question 22

Give an example of a transverse and longitudinal wave.

Answer 22

Anything on the electromagnetic spectrum, water waves, wave on a rope.
Sound wave
Seismic waves can be both.

Question 23

How does the wavelength of a stationary wave change as the frequency is tripled?

Answer 23

Wavelength decreases by a factor of 3 as frequency is inversely proportional to wavelength.

Question 24

What’s the difference between phase difference of two waves and the path difference?

Answer 24

Phase difference is given in degrees.

Path difference is given in fractions of a wavelength.