Interference: past paper questions
Real questions on interference
The newest 20 of 59 written questions. Open one to see it on the real paper.
- 9702/22 · October/November 2025 · Q4a[3]
Explain how the pattern of bright and dark fringes is formed.
See it on the paper → - 9702/22 · October/November 2025 · Q4c[1]
The double slit is removed. A second laser is placed beside the first laser. The second laser produces visible light of a different frequency from that of the first laser. The beams of light from the two lasers overlap on the screen. Explain why a steady pattern of bright and dark fringes is not formed on the screen.
See it on the paper → - 9702/23 · 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 → - 9702/23 · 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 → - 9702/23 · 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 → - 9702/21 · May/June 2025 · Q4b(i)[3]
Calculate D. D = m
See it on the paper → - 9702/21 · May/June 2025 · Q4b(ii)[3]
The slit separation is now gradually decreased from 0.16 mm to 0.04 mm. The distance between the centres of adjacent dark fringes is x. On Fig. 4.3, sketch the variation of x with slit separation. 1.6 1.2 x / cm 0.8 0.4 0 0 0.04 0.08 0.12 0.16 slit separation / mm
See it on the paper → - 9702/21 · October/November 2024 · Q5a(i)[2]
State the values of P, Q, R and S. P = R =
See it on the paper → - 9702/21 · October/November 2024 · Q6a(i)[2]
Explain why the position of greatest intensity is not at point O.
See it on the paper → - 9702/21 · October/November 2024 · Q6a(ii)[2]
On Fig. 6.1, draw a cross (×) to show the position of the point on line PQ where the intensity minimum that is the closest to point O occurs. Label this point B.
See it on the paper → - 9702/22 · May/June 2024 · Q6a[3]
number of bright fringes = (a) Determine the total number of bright fringes formed on the screen. ,
See it on the paper → - 9702/23 · May/June 2024 · Q4d[3]
The wave is a water wave produced by a dipper S 1 attached to a vibrator in a ripple tank. An identical dipper S 2 is attached to the same vibrator. The two dippers produce an interference pattern on the water in the tank, as shown in Fig. 4.3. water wave crests P wave troughs S 1 S 2 Fig. 4.3 (not to scale) The wave c...
See it on the paper → - 9702/22 · February/March 2024 · Q6a(i)[3]
Explain how the pattern of bright and dark interference fringes is formed.
See it on the paper → - 9702/22 · February/March 2024 · Q6a(ii)[3]
The distance between the centres of bright fringe X and bright fringe Y in the pattern is 10.2 mm. The slit spacing is 1.2 mm. The distance from the slits to the screen is 3.1 m. Calculate the wavelength of the light incident on the slits. wavelength = m
See it on the paper → - 9702/22 · February/March 2024 · Q6a(iii)[1]
The light is replaced by different visible light with a shorter wavelength. State how the new fringe separation will compare to the original fringe separation.
See it on the paper → - 9702/23 · October/November 2023 · Q5a(i)[1]
the position of an interference maximum (label this cross Y)
See it on the paper → - 9702/23 · October/November 2023 · Q5a(ii)[1]
the position of an interference minimum (label this cross Z).
See it on the paper → - 9702/23 · October/November 2023 · Q5b(i)[3]
Calculate the separation a of the sources A and B. a = m
See it on the paper → - 9702/21 · May/June 2023 · Q5b(ii)[3]
Calculate the separation a of the slits. a = m
See it on the paper → - 9702/21 · May/June 2023 · Q5c(i)[1]
Calculate the difference in the distances (the path difference) from each slit to the centre of fringe Q. difference in the distances = m
See it on the paper →
What examiners said
The majority of the candidates were able to draw a cross at an interference maximum. A significant number did not follow the instruction to label this cross Y. Some candidates gave only the letter Y without a cross and so the exact position of the maximum was difficult to estimate. Other candidates gave crosses but no labelling at all for both (i) and (ii).
— Examiner report, October/November 2023, 9702/23 Q5(a)(i) (Cambridge)
Candidates found it more difficult to show the position of an interference minimum. Many candidates put a cross on another interference maximum. A small number put crosses on Fig. 5.1 in a region where the wavefronts were not shown to be overlapping.
— Examiner report, October/November 2023, 9702/23 Q5(a)(ii) (Cambridge)
This question was very well answered by most of the candidates. A small number did not correctly convert the spacing of the interference maxima from centimetres to metres or made arithmetic errors when rearranging the relevant equation.
— Examiner report, October/November 2023, 9702/23 Q5(b)(i) (Cambridge)
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