double slit experiment

Question 1

Explain what is meant by a constant phase difference.

Answer 1

• same frequency
• same wavelength

Question 2

Explain what is meant by the term ‘coherent’.

Answer 2

• constant phase difference
• same frequency

Question 3

How do we ensure coherence for a non-coherent light source?

Answer 3

colour filter - filter out to one frequency
single slit - behaves as single source of light to get a constant phase difference

Question 4

State the relationship between amplitude and intensity.

Answer 4

higher the amplitude, highter the intensity

Question 5

What are the centre of bright fringes called & how are they produced?

Answer 5

• maxima
• produced by constructive interference

Question 6

What are the centre of dark fringes called & how are they produced?

Answer 6

• minima
• produced by destructive interference

Question 7

When are maximas formed?

Answer 7

when:
- path difference is an even number of 1/2 λ
- phase difference is an even multiple of π

Question 8

When are minimas formed?

Answer 8

when:
- path difference is an odd number of 1/2 λ
- phase difference is an odd multiple of π

Question 9

Explain how a maximum is formed at a point on the screen in the double-slit experiment.

Answer 9

a maximum is formed when two waves superpose to produce constructive interference
→ waves must arrive in phase (phase diff of even multiple of π)
→ (if initially in phase), they will arrive in phase if path difference is even number of 1/2 λ
→ this results in maximum possible amplitude, meaning that the stripe on the screen has maximum intensity.

Question 10

Explain how a minimum is formed at a point on the screen in the double-slit experiment.

Answer 10

a minimum is formed when two waves superpose to produce destructive interference
→ waves must arrive in antiphase (phase diff of odd number of π)
→ arrives in antiphase if path difference is an odd multiple of 1/2 λ
→ results in minimum possible amplitude, meaning that the stripe on the screen has minimum intensity.

Question 11

What happens to fringe spacing as distance to screen decreases?

Answer 11

decreases

Question 12

Why is a central white fringe produced when white light is used in a double slit experiment?

Answer 12

All the different wavelengths produce a central fringe, and these overlap to produce white light.

Question 13

Describe the fringe patten for white light.

Answer 13

• central white fringe
• rainbow fringes on either side
• from blue to red as we progress outwards from the centre