IB Physics HL C.3 Wave phenomena questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceMedium1 mark

A monochromatic beam illuminates two identical slits, each of width $a$ whose centres are separated by $d$ The ratio $d/a$ is an integer greater than 1. Which order of the two-slit interference pattern is absent because it coincides with the first minimum of the single-slit diffraction envelope?

Show answer and explanation

Answer: B. At the first single-slit minimum, $a\sin\theta=\lambda$ A missing interference maximum occurs at the same angle, where $d\sin\theta=n\lambda$ Equating the angles gives $n=d/a$

A: reverses the ratio of slit width to centre separation.
C: uses the first diffraction-minimum index as the interference order without matching the angles.
D: uses twice the first-minimum condition, introducing an extra factor of 2.

Remember: an interference order is missing when its maximum coincides with a diffraction minimum.

Question 2

Paper 2Medium9 marks

Two loudspeakers, $S_1$ and $S_2$ are connected to the same signal generator and emit sound in phase. Figure 1 shows measured distances from each loudspeaker to three positions on a detector’s path. The path lengths are measured to the nearest $0.01\ \text{m}$

(a)

Explain why the sources must be coherent for the maxima and minima of the interference pattern to remain in fixed positions.

[2]

(b)

P and Q are consecutive positions of maximum intensity.

(i)

Using Figure 1, calculate the path difference at P and at Q.

[2]

(ii)

Determine the wavelength of the sound.

[2]

(c)

Determine the order $n$ of constructive interference at R. Show your reasoning.

[3]

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