Chapter 12

Question 1

What is superposition?

Answer 1

A physical phenomenon where 2 waves meet and they overlap so that their displacements combine
When 2 wakes meet, the total displacement at a given point in time is the vector sum of the 2 individual displacements

Question 2

What happens when 2 waves continually pass through each other?

Answer 2

They superpose which creates a resultant wave

Question 3

What dictates the final magnitude of the superposed wave?

Answer 3

Phase difference and path length difference

Question 4

When does constructive interference occur?

Answer 4

When 2 waves that are in phase(even integer of pi) meet so the resultant displacement is of a higher displacement

Remember that intensity is proportional to amplitude^2

Question 5

When does destructive interference occur?

Answer 5

When 2 waves meet in antiphase(odd integer of pi), the max positive displacement adds to the max negative displacement so the resultant displacement is lower

Question 6

What happens if both waves have the same amplitude and they are in anti phase?

Answer 6

Resultant displacement is 0

Question 7

What is interference? When is it observed?

Answer 7

The effect observed when 2 or more waves superpose

Only observed when 2 COHERENT wave sources superpose

Question 8

What is a coherent wave source?

Answer 8

A wave source that maintains a constant phase difference throughout time and have the same frequency

Question 9

What are the 2 conditions for coherency?

Answer 9

Temporal coherency: waves have to be the same frequency

Spatial frequency: each source maintains the same displacement with regard to each other

Question 10

When can interference patterns of light only be observed?

Answer 10

When 2 coherent sources superpose

If the phase difference changes in time, it would be seen as a constant line

Question 11

What happens at maxima and minima?

Answer 11

At maxima, the waves interfere constructively

At minima the waves interfere destructively

Question 12

What is path length difference?

Answer 12

The difference in length in paths traveled by 2 difference waves. It is measured as a fraction of wavelengths

Question 13

What is constructive interference and destructive interference

Answer 13

Constructive: when path length difference is an integer of lamda and waves arrive in phase

Destructive: when path length difference is an odd multiple 1/2 of lamda like 1 half, 3 half

Question 14

What does Young’s double slit experiment show?

Answer 14

Light acts as a wave

Question 15

What is Young’s experiment?

Answer 15

Light from a lamp is passed through a colour filter so light is monochromatic (has the same frequency) and same wavelength

Light is passed through a single slit so it diffracts. It then arrives and passes through a double slit which produces 2 coherent wave sources that are in phase

Light miles forwards and interferes with each other which produces an interference pattern on a screen with bright and dark fringes

Question 16

What cause the bright fringes?

Answer 16

Constructive interference where light arrives in phase. Light from one slit overlaps with each other and superposes

Question 17

What causes the dark fringes?

Answer 17

Where light from one slit arrives in antiphase to light from the 2nd slit so they destructively interfere

Question 18

What is the formula for wavelength in this experiment?

Answer 18

Wavelength = slit separation x fringe seperation / distance between slit and screen

Question 19

What happens if you use a diffraction grating?

Answer 19

The pattern is really sharp because there are more beams interfering constructively. This means that fringes are also sharper

Question 20

What is the other formula for this experiment?

Answer 20

Distance between slits x sin(angle between incident angle and angle of maxima) = order(of maxima) x wavelength

Question 21

What does larger wavelength and smaller grating separation mean?

Answer 21

Larger wavelength means pattern spreads out more

Smaller grating means that there is less spreading out

Question 22

What happens if you shine white light instead of monochromatic light?

Answer 22

There is a colourful pattern because different wavelengths spread out different amounts

Question 23

What is a stationary wave?

Answer 23

A wave that oscillates in time but does not transfer any net energy

Question 24

When are stationary waves formed?

Answer 24

Formed from the superposition of 2 progressive waves of the same frequency and wavelength which propagate in opposite directions

Question 25

What is a node and an anti node?

Answer 25

A node is a point of 0 displacement where amplitude and intensity = 0. Also a point of destructive interference

An anti node is a point of maximum displacement where amplitude is max. Also a point of constructive interference

Question 26

What is the desperation between 2 adjacent nodes or anti nodes?

Answer 26

1/2 lamda

Question 27

What is the phase difference between adjacent nodes?

Answer 27

0. Particles oscillate in phase between adjacent nodes because when one particle hits maximum displacement, so do all of them

Question 28

What is the phase difference in different sides of a node?

Answer 28

Pi radians is the phase difference

Different sides of a node are in antiphase

Question 29

Differences between progressive and stationary wave?

Answer 29

Progressive transfers energy in direction of propagation but stationary doesn’t

Progressive wavelength is the distance between 2 points oscillating in phase. Stationary wavelength is the distance between 2 adjacent nodes x 2

All parts between nodes are in phase, on opposite sides of nodes are in antiphase

Stationary waves have max amplitude at anti node and none at node. Progressive waves have max amplitude everywhere

Question 30

What is the fundamental frequency?

Answer 30

The lowest resonant frequency (aka first harmonic)

Question 31

Which factors determine fundamental frequency?

Answer 31

Mass, tension and length

Question 32

What happens in an closed pipe?

Answer 32

The open end is an anti node and the closed end is a node

The length, density and temperature deter jong the fundamental frequency and wave speed

Only odd harmonics(odd multiples of the fundamental frequency) can form

Sound waves form stationary waves when reflected

Question 33

What happens in an open air pipe?

Answer 33

Both ends are open so both have anti nodes

Density, temperature, length determine fundamental frequency and wave speed

Each harmonic is a multiple of the fundamental frequency