Chapter 12 Waves 2

Question 1

How can stable interference be formed?

Answer 1

Must have coherence:

- 2 waves must have the same frequency and spatial coherency

Question 2

Why can’t filament lamp form a stable interference pattern?

Answer 2

• These emit a range of different frequencies and ever changing phase differences between waves
• So no frequency coherency

Question 3

What happens at Maxima and Minima?

Answer 3

• At Maxima, waves interfere constructively

- At Minima, waves interfere destructively

Question 4

What are the path difference rules?

Answer 4

• If path difference to a point is 0, or a WHOLE NUMBER of wavelengths, then there is constructive interference
• If the path difference to a point is an ODD NUMBER OF WAVELENGTHS, then there is destructive interference

Question 5

Describe the Young Double-Slit Experiment:

Answer 5

• Young used a monochromatic source of light and a narrow slit to diffract light
• Light diffracting from single slit arrives at double slit in phase
• Then diffracts again from the single slit
• Each slit acts as a source of coherent waves
• Leads to an interference pattern

Question 6

How is a stationary formed on a string?

Answer 6

• Wave travels to end and is reflected
• Reflected wave INTERFERES/SUPERPOSES with incident wave
• Always destructively/ constructively at certain points to produce nodes/antinodes

Question 7

What is phase difference?

Answer 7

• Relates to oscillation of 2 points on same wave

- How far ‘out of step’ one oscillation is from the other

Question 8

What is the principle of superposition?

Answer 8

When two(or more) waves interact (at a point) the (resultant) displacement is the (vector) sum of the 
(individual) displacements