CIE A Level Physics
CIE A Level Physics Superposition Exam Questions
Free CIE A Level Physics exam questions for Superposition, with a mark scheme for every pack. Covers stationary waves, diffraction, interference, coherence, Young's double-slit experiment and the diffraction grating.
Superposition exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About CIE A Level Physics Superposition
Superposition is Topic 8 of the Cambridge International AS & A Level Physics (9702) syllabus. It applies the principle of superposition to explain stationary waves, diffraction and interference. You study stationary waves on strings and in air columns, two-source interference with water waves, microwaves and light, the double-slit experiment and the diffraction grating. It follows directly from the Waves topic and returns in Quantum physics when electron diffraction is used as evidence for wave behaviour. Examiners test the conditions for observable interference, path difference arguments and calculations with λ = ax/D and d sin θ = nλ.
What you need to know
- Principle of superposition When two or more waves meet, the resultant displacement equals the sum of the individual displacements.
- Stationary waves Formed by two waves of the same frequency travelling in opposite directions. Adjacent nodes (or antinodes) are λ/2 apart; stationary waves can be used to measure wavelength and hence speed.
- Diffraction Spreading of a wave through a gap or around an edge, most noticeable when the gap is similar in size to the wavelength.
- Interference and coherence Sources are coherent if they have a constant phase difference. Constructive interference occurs for path difference nλ and destructive for (n + ½)λ when sources are in phase.
- Double-slit experiment Fringe separation x is given by λ = ax/D, where a is slit separation and D is the distance from slits to screen.
- Diffraction grating d sin θ = nλ, where d is the grating spacing. The maximum order is the largest whole number not exceeding d/λ.
Common mistakes in Superposition
- Saying nodes are one wavelength apart. Adjacent nodes are half a wavelength apart.
- Saying stationary waves transfer energy along the medium. Unlike progressive waves, they store energy and do not transfer it.
- Using lines per mm as d in the grating equation. Convert to spacing in metres: d = 1/(lines per metre).
- Saying coherent means the same amplitude. Coherent means a constant phase difference.
- Rounding up when finding the highest diffraction order. Take the integer part of d/λ, since sin θ cannot exceed 1.
Try three Superposition exam-style questions
1. In a double-slit experiment the slit separation is 0.50 mm, the screen is 2.0 m away and the fringe separation is 2.4 mm. Calculate the wavelength. (2 marks)
Show the mark scheme answer
λ = ax/D = (0.50 × 10^-3 × 2.4 × 10^-3)/2.0; λ = 6.0 × 10^-7 m.
2. Light of wavelength 600 nm falls normally on a grating with 300 lines per mm. Calculate the angle of the first order maximum and the highest order observed. (4 marks)
Show the mark scheme answer
d = 1/(3.0 × 10^5) = 3.33 × 10^-6 m; sin θ = λ/d = 0.18 so θ = 10.4°; d/λ = 5.6; highest order = 5.
3. Explain how a stationary wave is formed on a stretched string. (3 marks)
Show the mark scheme answer
A wave travels along the string and reflects at the fixed end; the incident and reflected waves have the same frequency and speed and travel in opposite directions; they superpose to give nodes and antinodes.
Superposition FAQs
What does Cambridge AS & A Level Physics Superposition cover?
It covers the principle of superposition, stationary waves, diffraction, two-source interference, coherence, the double-slit experiment and the diffraction grating.
Which papers is Superposition examined in?
It is an AS Level topic assessed in Paper 1 and Paper 2, and stationary wave and grating experiments are common practical contexts.
What equations do I need for Superposition?
Learn λ = ax/D for the double slit, d sin θ = nλ for the grating, and that nodes are λ/2 apart in a stationary wave.
