Particles and Waves: 5 - Interference

Question 1

When are waves in phase?

Answer 1

Two waves are IN PHASE when the same point of both waves arrive at the same point in space (peak/trough) at the same point.

Question 2

When are waves out of phase?

Answer 2

Two waves are EXACTLY OUT OF PHASE when opposite parts of both wave arrive at the same point in space (peak and trough) at the same point.

Question 3

What is interference evidence for?

Answer 3

Interference is evidence for the wave model of light.

Question 4

When can waves interfere?

Answer 4

When they are coherent.

Question 5

What does it mean for a wave to be coherent?

Answer 5

The waves have the same frequency (hence wavelength) the same speed and have a constant phase relationship?

Question 6

What are the 2 types of interference?

Answer 6

Destructive and Constructive.

Question 7

What dictates whether or not the interference of waves is constructive or destructive?

Answer 7

How the waves combine depends on how they are configured when they meet.

Question 8

How do the waves arrive in constructive interference?

Answer 8

The waves arrive in phase and produce a larger wave.

Question 9

How do waves arrive in destructive interference?

Answer 9

The waves arrive 180° out of phase and cancel each other out.

Question 10

What is the interference when 2 troughs meet?

Answer 10

Constructive

Question 11

What is the interference when 2 crests meet?

Answer 11

Constructive

Question 12

What is the interference when a trough and a crest meet?

Answer 12

Destructive

Question 13

What is the equation for the path difference for maximum?

Answer 13

m x λ

Question 14

What is the equation for the path difference for minimum?

Answer 14

(m + 1/2) x λ

Question 15

What is the diffraction grating equation for constructive interference?

Answer 15

mλ = d x sinθ

Question 16

What is the diffraction grating equation for destructive interference?

Answer 16

(m + 1/2)λ = d x sinθ

Question 17

When a white light source is used to produce an interference pattern with a prism, what is observed/seen?

Answer 17

Only one spectrum is produced (going from red at the top to violet at the bottom).

Red is deviated least with violet being the most deviated.

The image is very bright.

Question 18

When a white light source is used to produce an interference pattern with a diffraction grating, what is observed/seen?

Answer 18

The central maximum is white.

There is more than one spectrum going from violet to red.

Red is deviated most, violet least (red light wavelength is longest hence diffracts the most).

Spectra are less intense.