Chapter 12: Superposition

Question 1

State the Principle of Superposition

Answer 1

When waves meet, the actual displacement is the vector sum of the separate displacements of the individual waves, and each wave proceeds as though no other waves exist

Question 2

Define interference

Answer 2

Interference is the result of superposition of wavetrains from a finite number of coherent sources

Question 3

What are coherent sources?

Answer 3

Coherent sources are sources that have a constant phase difference

Question 4

Define constructive interference

Answer 4

When two waves meet in phase at a point, they reinforce each other, and the resultant amplitude of the wave is a maximum. The waves are said to interfere constructively.

Question 5

Define destructive interference.

Answer 5

When two waves meet in antiphase or exactly π radians out of phase at a point, they cancel each other and the resultant amplitude of the wave is a minimum. The waves are said to interfere destructively.

Question 6

Define path difference

Answer 6

The path difference between two wavetrains is the extra length that the wave from one source must travel, compared to the wave from the other source, in order to reach the point of observation.

Question 7

What is a stationary wave?

Answer 7

A stationary wave is formed from the superposition of two progressive wavetrains of equal amplitude and frequency (and therefore wavelength) travelling with the same speed in opposite
directions over the same space.

Question 8

Define diffraction

Answer 8

Diffraction is the spreading of waves when they pass through an opening or around an
obstacle.

Question 9

State the Rayleigh criterion

Answer 9

Rayleigh’s criterion says the images of two point sources can just barely be distinguished from each other (resolved) if the central maximum of one diffraction pattern falls on the first minimum of
the other one.