Chapter 12- Waves 2

Question 1

When does superposition happen?

Answer 1

When two waves of the same type meet, either because they are going in opposite directions or one overtakes the other
They continue as they were otherwise

Question 2

Principle of superposition

Answer 2

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 3

Constructive interference

Answer 3

When the two waves are exactly in phase, the combined wave has an amplitude equal to the sum of the amplitude of each

Question 4

Destructive interference

Answer 4

When two waves are in anti-phase, the waves cancel each other out so the resultant displacement is 0m

Question 5

Coherence

Answer 5

The waves have the same frequency and constant phase difference so the interference pattern will be regular

Question 6

Path difference

Answer 6

The difference in the distances travelled by the waves

Question 7

Path difference -> phase difference

Answer 7

Replace λ with π and double the coefficient

Question 8

Node vs anti-node

Answer 8

In a standing wave, a node has 0 displacement and an anti-node maximum displacement

Question 9

1st order minima

Answer 9

π or λ/2

Question 10

1st order maxima

Answer 10

2π or λ

Question 11

Path difference at a maxima

Answer 11

nλ

The waves are in phase

Question 12

Path difference at a minima

Answer 12

(2n-1)λ/2

The waves are in anti-phase

Question 13

Stationary waves

Answer 13

Produced by superposition of two progressive waves of equal amplitude and frequency, travelling with the same speed in opposite directions.

Question 14

Stationary wave characteristics

Answer 14

Varying amplitude
Doesn’t transfer energy
In phase between nodes, in anti-phase either side of one

Question 15

Young’s Double slit experiment

Answer 15

Pass an incoherent light source through a single slit or use a coherent light source
Then put a double slit in front with a screen a large distance behind

Question 16

Young’s Double slit wavelength equation

Answer 16

ax
λ = ——–
D
Where a is the distance between the slits, x the distance between the first and second maxima and D from the double slit to the screen

Question 17

Why does Young’s double slit experiment produce that pattern?

Answer 17

It passes a coherent wave through a double slit which causes it to diffract
Where the path difference is an integer coefficient of the wavelength there will be constructive interference and a maxima

Question 18

Distance between a neighbouring node and anti-node in a standing wave

Answer 18

λ/4

Question 19

Standing waves on strings

Answer 19

They have a fixed point at either end so there will be a node at each end

Question 20

Amount of nodes in the 2nd harmonic

Answer 20

1 in between the two at the end

Question 21

Amount of nodes in the 3rd harmonic

Answer 21

2 in between the two at the end, it increases by 1 each time

Question 22

Fundamental frequency

Answer 22

f0, the minimum frequency of a stationary wave of a harmonic, produces the 1st harmonic with no nodes in the middle

Question 23

Finding the wavelength from a harmonic

Answer 23

λ = 2L/n

Where b is the harmonic number, and L the length of the string

Question 24

Frequency of a harmonic

Answer 24

f = n(f0)

Where n is the harmonic number

Question 25

Stationary wave vs progressive waves

Answer 25

• progressive waves transfer energy through space, standing do not
• phase varies constantly along a progressive wave, in a standing wave all points between two nodes are in phase
• the frequency/wavelength of a standing wave is equal to that of the progressive waves that form it

Question 26

What affects the pitch of a sound?

Answer 26

Tension
Length of string
Thickness of string

Question 27

Nodes and anti-nodes on a longitudinal standing wave

Answer 27

They are in terms of the displacement of particles, nodes on a longitudinal wave are where particles arent moving

Question 28

Standing waves on tubes

Answer 28

There is always a node at a closed end and an anti-node at an open end

Question 29

Fraction of a wavelength in a tube with two open ends

Answer 29

n λ
——-
2

Where n is the harmonic number

Question 30

Fraction of a wave in a tube with one open and one closed end

Answer 30

(2n-1) λ
———
4
Where n is the harmonic number

Question 31

Phase in standing waves

Answer 31

Points are in phase if they are between 2 nodes