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Question 23M.2.SL.TZ2.3

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Date May 2023 Marks available [Maximum mark: 9] Reference code 23M.2.SL.TZ2.3
Level SL Paper 2 Time zone TZ2
Command term Calculate, Explain, Predict Question number 3 Adapted from N/A
3.
[Maximum mark: 9]
23M.2.SL.TZ2.3

Blue light of wavelength λ is incident on a double slit. Light from the double slit falls on a screen. A student measures the distance between nine successive fringes on the screen to be 15 cm.

The separation of the double slit is 60 µm; the double slit is 2.5 m from the screen.

(a)

Explain the pattern seen on the screen.

[3]

Markscheme

Mention of interference / superposition ✓

Bright fringe occurs when light from the slits arrives in phase ✓

Dark fringe occurs when light from the slits arrives 180°/ π out of phase ✓

(b)

Calculate, in nm, λ.

[3]

Markscheme

s = 0.158  OR = 0.0188 «m» ✓

use of λ=dsD ✓

450 «nm» ✓

(c)

The student changes the light source to one that emits two colours:
• blue light of wavelength λ, and
• red light of wavelength 1.5λ.

Predict the pattern that the student will see on the screen.

[3]

Markscheme

Blue fringe is unchanged ✓

Red fringes are farther apart than blue ✓

By a factor of 1.5 ✓

At some point/s the fringes coincide/are purple ✓

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