Diffraction: past paper questions
Real questions on diffraction
The newest 20 of 22 written questions. Open one to see it on the real paper.
- 9702/21 · October/November 2025 · Q4a[2]
State what is meant by diffraction of a wave.
See it on the paper → - 9702/23 · October/November 2025 · Q4a[2]
State what is meant by diffraction of a wave.
See it on the paper → - 9702/23 · 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 → - 9702/23 · May/June 2025 · Q6a[1]
State what is meant by diffraction.
See it on the paper → - 9702/22 · October/November 2023 · Q5b[2]
State what is meant by the diffraction of a wave.
See it on the paper → - 9702/41 · May/June 2023 · Q7b(i)[1]
State the name of the phenomenon demonstrated by the pattern shown in Fig. 7.2.
See it on the paper → - 9702/41 · May/June 2023 · Q7b(ii)[2]
Explain what can be concluded from the pattern in Fig. 7.2 about the nature of electrons.
See it on the paper → - 9702/23 · May/June 2022 · Q5b(iii)[4]
The beam from the laser now passes through a diffraction grating with 2400 lines per millimetre. A detector sensitive to the waves emitted by the laser is moved through an arc of 180° in order to detect the maxima produced by the waves passing through the grating, as shown in Fig. 5.2. detector laser diffraction gratin...
See it on the paper → - 9702/23 · May/June 2022 · Q5b(iv)[2]
The laser is now replaced with one that emits electromagnetic waves with a wavelength of 300 nm. Explain, without calculation, what happens to the number of maxima now detected. Assume that the detector is also sensitive to this wavelength of electromagnetic waves.
See it on the paper → - 9702/21 · May/June 2021 · Q4c[2]
The light from the laser is incident normally on a diffraction grating. Describe the diffraction of the light waves at the grating.
See it on the paper → - 9702/21 · May/June 2021 · Q4d(i)[2]
The gradient of the graph is G. Determine an expression, in terms of G, for the distance d between the centres of two adjacent slits in the diffraction grating. d =
See it on the paper → - 9702/21 · May/June 2021 · Q4d(ii)[2]
On Fig. 4.1, sketch a graph to show the results that would be obtained for the second-order maxima.
See it on the paper → - 9702/22 · October/November 2020 · Q5b(i)[1]
the path difference path difference = m
See it on the paper → - 9702/41 · May/June 2020 · Q6a(i)[1]
Suggest an advantage of greater bandwidth.
See it on the paper → - 9702/41 · May/June 2020 · Q6b[2]
In telecommunications, a signal power of 1.0 mW is used as a reference power. Signal powers relative to this reference power and expressed in dB are said to be measured in ‘dBm’. Show that a signal power of 13 dBm is equivalent to 20 mW.
See it on the paper → - 9702/41 · May/June 2020 · Q6c[2]
A signal of input power 20 mW is transmitted along an optic fibre for an uninterrupted distance of 45 km. The optic fibre has an attenuation per unit length of 0.18 dB km –1 . Calculate the output power P from the optic fibre. P = mW
See it on the paper → - 9702/23 · October/November 2019 · Q5b(ii)[1]
State and explain the change, if any, to the distance between the second order maximum spots on the screen when the light from the laser is replaced by light of a shorter wavelength.
See it on the paper → - 9702/22 · May/June 2019 · Q4c(i)[2]
Monochromatic light is incident on a diffraction grating. Describe the diffraction of the light waves as they pass through the grating.
See it on the paper → - 9702/22 · May/June 2019 · Q4c(ii)[3]
A parallel beam of light consists of two wavelengths 540 nm and 630 nm. The light is incident normally on a diffraction grating. Third-order diffraction maxima are produced for each of the two wavelengths. No higher orders are produced for either wavelength. Determine the smallest possible line spacing d of the diffrac...
See it on the paper → - 9702/22 · May/June 2019 · Q4c(iii)[2]
The beam of light in (c)(ii) is replaced by a beam of blue light incident on the same diffraction grating. State and explain whether a third-order diffraction maximum is produced for this blue light.
See it on the paper →
What examiners said
It was usually stated correctly that diffraction takes place when a wave passes through an aperture or by an edge. Candidates also needed to state that this causes the wave to spread (into the geometrical shadow). Candidates should be encouraged to avoid using the term ‘bend’ instead of ‘spread’ as that could be describing refraction or reflection.
— Examiner report, October/November 2023, 9702/22 Q5(b) (Cambridge)
The majority of candidates correctly stated electron diffraction here. Some candidates referred to the photoelectric effect, the production of X-rays or other phenomena showing they were not familiar with the diffraction of electrons.
— Examiner report, May/June 2023, 9702/41 Q7(b)(i) (Cambridge)
The question asked candidates what could be concluded from the pattern in Fig. 7.2. To be awarded full credit, candidates had to explain that the pattern was indicating diffraction and go from there to explaining that therefore the electrons must be behaving as waves. Candidates often were given credit for stating that electrons were behaving as waves but very rarely explained the pattern.
— Examiner report, May/June 2023, 9702/41 Q7(b)(ii) (Cambridge)
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