Flashcards in Chapter 12 Waves 2 Deck (33):

1

## What is the principle of superposition?

### 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.

2

## What is constructive interference?

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

3

## What is destructive interference?

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

4

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

### The overall amplitude will be 0

5

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

### 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.

6

## What is coherence?

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

7

## What can be deduced from coherant waves?

### The two waves have the same frequency

8

## What is a maxima?

### This is the point of maximum constructive interference

9

## What is a minima?

### This is the point of minimum constructive interferance

10

## What is a path difference?

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

11

## What is known about the path difference of a maxima?

### The path difference is a whole number of wavelengths

12

## What is know about the path difference of a minima?

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

13

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

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

14

## What are the units / measurements of phase difference?

### Either wavelength or degrees or radians

15

## What is monochromatic light?

### This is light that is all one frequency

16

## What is youngs two slit experiment?

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

17

## What did Youngs two slit experiment show?

### It showed that light was a wave

18

## What is the equation for youngs two slit experiment?

###
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

19

## What is a stationary wave?

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

20

## What is a node and antinode?

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

21

## The separation between two nodes is...

### equal to the wavelength

22

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

### Stationary waves do not transfer energy

23

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

###
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

24

## What is the fundamental frequency?

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

25

## What is a harmonic?

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

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

###
1: 20Hz 2Lλ f0

2: 40Hz Lλ 2f0

3: 60Hz 1.5Lλ 3f0

4: 80Hz 0.5Lλ 4f0

5: 100Hz 2/5Lλ 5f0

27

## Why do harmonics occur?

### 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

28

## How is a stationary wave formed with sound?

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

29

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

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

30

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

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

31

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

### 4x the length of the tube

32

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

### 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

33