Chapter 12 - Wave 2

Question 1

What happens when two waves superpose?

Answer 1

The resultant displacement can be greater or lesser than initial displacement

Question 2

What dictates the magnitude of the final displacement of the superposed wave?

Answer 2

The phase difference between them

Question 3

What happens to the magnitude of the final displacement if they are in phase?

Answer 3

There will be maximum positive displacement
Constructive interference (Even multiples of pi)

Question 4

What happens to the displacement if the waves are antiphase?

Answer 4

The waves cancel out
Destructive Interference (Odd multiples of pi)

Question 5

What is interference?

Answer 5

Interference is the pattern that is observed when superposition takes place

Question 6

Practically, when can interference effect be observed?

Answer 6

In practice, interference effects are only observed when two coherent wave sources superpose

Question 7

What are coherent wave sources?

Answer 7

Coherent wave sources are those that maintain a constant phase difference, at a point in space, with respect to time

Question 8

What properties must a coherent wave source have?

Answer 8

Constant phase difference
Same Frequency

Question 9

Why are sound wave interference patterns easily observed?

Answer 9

Large wavelengths
Slow wave speed

Question 10

When are interference patterns of light observed?

Answer 10

When two coherent sources of light waves superpose

Question 11

What is the path length difference?

Answer 11

The path length difference between two waves is the difference in length in the paths travelled by each wave

Question 12

What must PLD and phase difference be for coherent wave sources?

Answer 12

PLD must be a fraction of the wavelength of the waves
PLD must directly correlate to the phase difference between two waves

Question 13

What must PLD and phase difference be for constructive interference?

Answer 13

PLD of even multiple of wavelength///2
Phase difference of multiple of 2pi

Question 14

What must PLD and phase difference be for destructive interference?

Answer 14

PLD of odd multiple of wavelength///2
Phase difference of odd multiple of pi

Question 15

What is coherency?

Answer 15

Coherency is the potential for two waves to interact

Question 16

What is the set up for the young double split experiment?

Answer 16

Lamp
Colour Filter
Narrow Single Slit
Double Slits
Screen
Interference Fringe

Question 17

Why is light put through the colour filter?

Answer 17

Colour filter produces a monochromatic source of light which limits the light to the same frequencies

Question 18

Why is a single slit used?

Answer 18

A single slit diffracts to illuminate the double slit. The narrow slit ensures the light is of constant phase difference

Question 19

Why are double slits used?

Answer 19

The double slit produces two sources of coherent waves

Question 20

What happens after the double slits?

Answer 20

The light from each slit moves forward, they overlap and superpose, producing dark and bright fringes

Question 21

What are dark and bright spots produced by?

Answer 21

Light waves in phase make bright fringes as they constructively interfere
Antiphase light waves make dark fringes they destructively interfere

Question 22

What are the variables in this practical?

Answer 22

Distance between slits and screens (D)
Slit separation (a)
Wavelength of incident light (y)
Fringe separation (x)

Question 23

What is the formula for the relationships between the young double slit experiment?

Answer 23

y = ax / d

Wavelength = (Slit separation x Fringe separation) /// Distance between slits and screen

Question 24

In what situation does this formula work?

Answer 24

The formula only works when a < D significantly