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Date May 2017 Marks available 2 Reference code 17M.2.SL.TZ1.2
Level Standard level Paper Paper 2 Time zone Time zone 1
Command term Outline Question number 2 Adapted from N/A

Question

Outline what is meant by the principle of superposition of waves.

[2]
a.

Red laser light is incident on a double slit with a slit separation of 0.35 mm.
A double-slit interference pattern is observed on a screen 2.4 m from the slits.
The distance between successive maxima on the screen is 4.7 mm.

Calculate the wavelength of the light. Give your answer to an appropriate number of significant figures.

[3]
b.

Explain the change to the appearance of the interference pattern when the red-light laser is replaced by one that emits green light.

[2]
c.

One of the slits is now covered.

Describe the appearance of the pattern on the screen.

[2]
d.

Markscheme

when 2 waves meet the resultant displacement

is the «vector» sum of their individual displacements

 

Displacement should be mentioned at least once in MP 1 or 2.

a.

λ = \(\frac{{4.7 \times {{10}^{ - 3}} \times 0.35 \times {{10}^{ - 3}}}}{{2.4}}\)

= 6.9 x 10–7 «m»

answer to 2 SF

 

Allow missed powers of 10 for MP1.

b.

green wavelength smaller than red

fringe separation / distance between maxima decreases

 

Allow ECF from MP1.

c.

bright central maximum

subsidiary maxima «on either side»

 

the width of the central fringe is twice / larger than the width of the subsidiary/secondary fringes/maxima

OR

intensity of pattern is decreased

 

Allow marks from a suitably labelled intensity graph for single slit diffraction.

d.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.
[N/A]
d.

Syllabus sections

Core » Topic 4: Waves » 4.3 – Wave characteristics
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