Chapter 6: Wave Behaviour

Question 1

What is a wave?

Answer 1

A disturbance by which energy is transferred.

Question 2

Name the three characteristic properties of a wave

Answer 2

Reflection, refraction and diffraction.

Question 3

What is a standing wave?

Answer 3

The resultant when two coherent waves travel in opposite directions.

Question 4

What is a node?

Answer 4

A point on the standing wave which maintains a constant resultant amplitude of 0

Question 5

What is an antinode?

Answer 5

A point on the standing wave which is half a wavelength from the nodes and which always has an amplitude of twice those of its constituing waves.

Question 6

In a pipe with one end closed, what part of a standing wave is at either end of the pipe?

Answer 6

At the closed end there is a fixed node and at the open end there is a fixed antinode.

Question 7

In an open pipe, what part of the standing wave is at either end of the pipe?

Answer 7

Both ends have a fixed antinode

Question 8

What is the fundamental frequency of a standing wave (for a wave travelling with speed v in a box of length L)?

Answer 8

f=v/2L

Question 9

What is a phasor?

Answer 9

A geometrical representation of a wave - they consist of a circle

Question 10

What is the amplitude of a phasor at time t represented by?

Answer 10

A = a.sin(2πft)

Question 11

describe how colours arise in soap bubbles

Answer 11

Consider a layer of a translucent material with a thin layer of another material on top of it. Some incoming rays of are reflected from the first thin film surface whilst others refract through the surface and are only reflected when they reach the second layer. The two rays emerge from the film slightly out of phase with each other and interfere. If the path difference between the two rays is 2nλ+0.5, the waves are in antiphase and interfere destructively implying that some colours are missing. However, if the path difference is 2nλ, the waves will be in phase and will interfere constructively, making some colours stronger.

Question 12

What happens when a wave passes through a narrow slit (slit aperture comparable to the wavelength of the wave)?

Answer 12

The wave diffracts - spreads out - through the slit.

Question 13

What is a diffraction grating?

Answer 13

A series of parallel lines and gaps which are very close to each other. The closer the lines and gaps, the further spread out a beam becomes.

Question 14

What is the diffraction slit separation equation?

Answer 14

d.sinθ=nλ

Question 15

What is the diffraction aperture separation equation?

Answer 15

a.sinθ=nλ