Waves

Question 1

What is a wave?

Answer 1

Where energy is transferred some distance without any transfer of material between the two points.

Question 2

Amplitude

Answer 2

The maximum displacement of particles from equilibrium

Question 3

Wavelength

Answer 3

The distance between adjacent particles vibrating in phase

Question 4

Frequency

Answer 4

Number of waves passing a point / being given out by the sourse each second

Question 5

Time period

Answer 5

Time for a wave particle to do one cycle

Question 6

In phase

Answer 6

Where two waves are at the same point in their cycles at the same time

Question 7

Antiphase

Answer 7

Where two waves are half a cycle out of phase

Question 8

Transverse waves

Answer 8

Particles vibrate at right angels to the direction of energy transfer

Question 9

What is an EM wave?

Answer 9

A disturbance in the electric and magnetic field (these are perpendicular to each other and are always in phase)

Question 10

Properties of Em waves

Answer 10

• Can travel through a vacuum
• All travel at the speed of light in a vacuum

Question 11

EM waves in order of increasing wavelength (decreasing frequency)

Answer 11

Gamma
X-ray
UV
Visible
Infra-red
Micro
Radio

Question 12

Longitudinal waves

Answer 12

Vibrations are parallel to the direction of propagation of the wave

Question 13

Polarised light

Answer 13

Vibrates in only one direction perpendicular to the direction of travel of the light

Question 14

Unpolarised light

Answer 14

Vibrates in all directions perpendicular to the direction of travel of the light

Question 15

How can light be polarised?

Answer 15

With a polarising filter which polarises the light in one direction

Question 16

How can you distinguish between longitudinal and transverse waves?

Answer 16

Polarisation.
Only transverse waves can be polarised

Question 17

Which direction are fishermen’s glasses polarised in?

Answer 17

Polarised in the vertical direction to block light that is horizontally polarised by reflecting off the water

Question 18

Superposition

Answer 18

When two waves meet the total displacement at a point is equal to the sum of the individual displacements at that point

Question 19

What happens when two waves meet and are in phase with each other?

Answer 19

Reinforcement (constructive interference)

Question 20

What happens when two waves meet and are in anti-phase with each other?

Answer 20

Cancellation (destructive interference)

Question 21

Conditions for stationary / standing waves to form

Answer 21

Two waves must:
- Be moving in opposite directions
- Have the same frequency
- Have similar amplitudes
- Meet and superpose

Question 22

Nodes

Answer 22

Points where the displacement is always 0, waves meet in anti-phase and destructively interfere.

Question 23

Distance between two nodes or two anti-nodes

Answer 23

1/2 a wavelength

Question 24

Antinodes

Answer 24

Points where the amplitude of vibration is at its maximum, waves meet in phase and constructively interfere.

Question 25

Phase difference between two nodes

Answer 25

0 radians (in phase)

Question 26

Phase difference either side of a node

Answer 26

π radians (antiphase)

Question 27

Where are the nodes/antinodes of the harmonics on a string?

Answer 27

There is a node at each end

Question 28

Length of the 1st harmonic on a string / pipe with open ends

Answer 28

λ/2

Question 29

Length of the 1st harmonic in a pipe with one closed end

Answer 29

λ/4

Question 30

Why do microwave have turntables?

Answer 30

This moves the food through the nodes (no energy transfer) and antinodes (maximum energy transfer) to ensure it is evenly cooked.

Question 31

Features of progressive waves

Answer 31

- Energy is transferred - Adjacent particles vibrate out of phase - Adjacent particles have the same amplitude

Question 32

Features of standing waves

Answer 32

- Energy is trapped in one place - Adjacent particles are in phase with each other - Adjacent particles have a different amplitude

Question 33

What factors effect the first harmonic of a wave on a string?

Answer 33

- Tension - Mass per unit length of the string - Length of the vibrating string