The diffraction grating: past paper questions
Real questions on the diffraction grating
The newest 11 of 11 written questions. Open one to see it on the real paper.
- 9702/21 · October/November 2025 · Q4b(i)[2]
Show that the angle θ at which the first-order bright fringe is formed is 6.2°.
See it on the paper → - 9702/21 · October/November 2025 · Q4b(ii)[1]
Determine the value of θ at which the second-order bright fringe is formed. θ = °
See it on the paper → - 9702/21 · October/November 2025 · Q4b(iii)[3]
On Fig. 4.2, sketch the variation of the intensity I with θ for values of θ from –15° to +15°. 2I 0 I I 0 –15 –10 –5 0 0 5 θ / ° 10 15
See it on the paper → - 9702/21 · October/November 2025 · Q4c[2]
A polarising filter is placed in the path of the light beam that is incident on the diffraction grating in Fig. 4.1. The transmission axis of the filter is at 45° to the vertical. Suggest how the variation of intensity with θ for the light on the screen compares with the answer in (b)(iii).
See it on the paper → - 9702/23 · May/June 2025 · Q6b(ii)[3]
Calculate the number of lines per unit length in the diffraction grating. number per unit length = m −1
See it on the paper → - 9702/23 · May/June 2025 · Q6b(iii)[2]
The light in Fig. 6.1 is now replaced with light of a different wavelength λ. It is observed that the third-order maxima of this light are at the same positions as the second-order maxima of the light in Fig. 6.1. Calculate, in nm, the wavelength λ. λ = nm
See it on the paper → - 9702/22 · October/November 2023 · Q5c(i)[2]
Calculate the line spacing d of the diffraction grating. d = m
See it on the paper → - 9702/22 · October/November 2023 · Q5c(ii)[2]
Determine a different wavelength of visible light that will also produce a diffraction maximum at an angle of 68°. wavelength = m
See it on the paper → - 9702/23 · October/November 2021 · Q5c(i)[2]
Determine an expression, in terms of G and λ , for the separation a of the slits. a =
See it on the paper → - 9702/23 · October/November 2021 · Q5c(ii)[2]
The experiment is repeated with slits of separation 2a. The wavelength of the light is unchanged. On Fig. 5.2, sketch a graph to show the results of this experiment.
See it on the paper → - 9702/23 · October/November 2019 · Q5b(i)[2]
Determine the wavelength of the light. wavelength = m
See it on the paper →
What examiners said
Generally, this question was well answered. Weaker candidates were sometimes unable to recall the correct symbol equation or made inappropriate attempts to apply the symbol equation for the double-slit interference of light.
— Examiner report, October/November 2023, 9702/22 Q5(c)(i) (Cambridge)
This question was challenging and a significant number of the weaker candidates left the calculation and answer spaces blank. A common mistake was to calculate the same wavelength of 430 nm instead of a different wavelength. Other candidates sometimes calculated a different wavelength, but not one of visible light.
— Examiner report, October/November 2023, 9702/22 Q5(c)(ii) (Cambridge)
The majority of the candidates could recall the relevant symbol formula for double-slit interference using light. However, weaker candidates were often unable to relate that formula to the gradient of the graph.
— Examiner report, October/November 2021, 9702/23 Q5(c)(i) (Cambridge)
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