Chapter 12 Waves 2

Question 1

What is the principle of superposition?

Answer 1

This is when two waves overlap, they superpose. When two waves meet at a point the resultant displacement at that point is equal to the sum of the displacements of the individual waves.

Question 2

What is constructive interference?

Answer 2

This is when the displacement of the two meeting waves produces a higher displacement and so increases the amplitude

Question 3

What is destructive interference?

Answer 3

This is when the displacement of the two meeting waves produces a lower displacement so decrease the amplitude

Question 4

If the two waves have the same amplitude but the oposite displacements, what will happen?

Answer 4

The overall amplitude will be 0

Question 5

What can be seen with ripples in a pond from two sources?

Answer 5

An interference pattern can be seen. Where the waves are in phase there is constructive interference and where waves are out of phase there is destructive interference.

Question 6

What is coherence?

Answer 6

This is when two waves from two sources have a constant phase difference

Question 7

What can be deduced from coherant waves?

Answer 7

The two waves have the same frequency

Question 8

What is a maxima?

Answer 8

This is the point of maximum constructive interference

Question 9

What is a minima?

Answer 9

This is the point of minimum constructive interferance

Question 10

What is a path difference?

Answer 10

This is the difference in the distances each wave from two different sources has travelled

Question 11

What is known about the path difference of a maxima?

Answer 11

The path difference is a whole number of wavelengths

Question 12

What is know about the path difference of a minima?

Answer 12

The path difference is half a wavelength. e.g. 1.5λ or 5.5λ

Question 13

What is the central maxima and what is known about it?

Answer 13

It is the middle maxima where the path difference between the waves is 0λ and is equidistance between the two sources

Question 14

What are the units / measurements of phase difference?

Answer 14

Either wavelength or degrees or radians

Question 15

What is monochromatic light?

Answer 15

This is light that is all one frequency

Question 16

What is youngs two slit experiment?

Answer 16

This is when a single source of monochromatic light is shone diffracts through two slits that then cause an interference pattern on a screen

Question 17

What did Youngs two slit experiment show?

Answer 17

It showed that light was a wave

Question 18

What is the equation for youngs two slit experiment?

Answer 18

λ = ax / D
λ = wavelength
a = the slit separation
x = the difference between maxima on the screen
D = distance between the screen and the two slits

Question 19

What is a stationary wave?

Answer 19

This is the product of two progressive waves that constructively interfere and appears to be stationary

Question 20

What is a node and antinode?

Answer 20

A node is the point on a stationary wave where there is no displacement. An antinode is the point of maximum dispalcement

Question 21

The separation between two nodes is…

Answer 21

equal to the wavelength

Question 22

What is special about a stationary wave verses a progressive wave?

Answer 22

Stationary waves do not transfer energy

Question 23

What can be said about the phase of particles along a stationary wave?

Answer 23

Between two nodes all the particles are in phase, they all reach there maxima at the same time but their amplitudes are different.
On different sides of a node, the particles are in antiphase

Question 24

What is the fundamental frequency?

Answer 24

This is the minimum frequency for a stationary wave on a string

Question 25

What is a harmonic?

Answer 25

This is the different frequencies that form a stationary wave on a string. They are related to the fundamental frequency

Question 26

What is the wavelength, frequency and frequency as a multiple of f0 for the first 5 harmonics of a string with a fundamental frequency of 20Hz

Answer 26

1: 20Hz 2Lλ f0
2: 40Hz Lλ 2f0
3: 60Hz 1.5Lλ 3f0
4: 80Hz 0.5Lλ 4f0
5: 100Hz 2/5Lλ 5f0

Question 27

Why do harmonics occur?

Answer 27

Because there has to be a node at either end and then the length of the string does not change so the amount that the string can be divided into is limited

Question 28

How is a stationary wave formed with sound?

Answer 28

A speaker is faced against a solid surface. This causes a node to be formed where the solidsurface is

Question 29

Why is there a node formed at the end of a tube that is closed at one end?

Answer 29

Because the air at the end cannot move because it is against a wall. So therefore it forms a node

Question 30

What do we know about a stationary wave in a tube with a closed end?

Answer 30

There is a node at the closed and an antinode at the open end

Question 31

What is the wavelength of the first harmonic of a stationary wave formed in a tube with a closed end

Answer 31

4x the length of the tube

Question 32

What are the harmonics of a tube with a closed end?

Answer 32

They are all odd multiples of the fundamental frequency because that would require a antinode to form at the closed end which isn’t possible

Question 33

What happens with stationary waves in an open tube?

Answer 33

An antinode forms at each end

All integer multiples of f0 can be made