Unit 3 - Interference

Question 1

What condition must be met for two waves to be coherent

Answer 1

They must have a constant phase relationship.

Question 2

What conditions must be met for two waves travelling in air to have a constant phase relationship

Answer 2

They must have the same wavelength and frequency

Question 3

Describe constructive interference

Answer 3

Constructive interference is where two coherent waves meet exactly in phase to combine to produce a wave of larger amplitude

Question 4

Describe destructive interference

Answer 4

Destructive interference is where two coherent waves meet exactly out of phase to combine to produce a wave of zero amplitude

Question 5

Describe the phase change that occurs when a wave enters a different medium

Answer 5

A wave experiences a phase change of pi when it is travelling in a less
dense medium and reflects from an interface with a more dense medium.

A wave does not experience a phase change when it is travelling in a more dense medium and reflects from an interface with a less dense medium.

Question 6

Describe what is meant by division of amplitude

Answer 6

Division of amplitude is a process by which the amplitude of the incident beam is divided into two (or more) parts either by partial reflection or refraction. The two beams travel different paths and are finally brought together to produce interference.

Question 7

Explain what is meant by division of wavefront

Answer 7

Division of wavefront is where light is incident on two small slits, the wavefront is divided and each slit acts as a secondary source. Interference then takes place between the two secondary sources.