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Question 23M.2.HL.TZ2.3

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Date May 2023 Marks available [Maximum mark: 11] Reference code 23M.2.HL.TZ2.3
Level HL Paper 2 Time zone TZ2
Command term Calculate, Discuss, Explain, Predict Question number 3 Adapted from N/A
3.
[Maximum mark: 11]
23M.2.HL.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.i)

Calculate, in nm, λ.

[3]

Markscheme

s = 0.158  OR = 0.0188 «m» ✓

use of λ=dsD ✓

450 «nm» ✓

(b.ii)

The student moves the screen closer to the double slit and repeats the measurements. The instruments used to make the measurements are unchanged.

Discuss the effect this movement has on the fractional uncertainty in the value of λ.

[2]

Markscheme

«As the measurements decrease» the fractional uncertainty in D/s increases. ✓

«Fractional uncertainties are additive here» so fractional uncertainty in λ increases ✓

Answers can be described in symbols e.g. Δs/s

(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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