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.

Type

Multiple choice Written

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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]

Question 3

Paper 2Hard10 marks

In a laboratory, a laser illuminates both slits of a double-slit plate at normal incidence. The separation of adjacent bright fringes is measured on a screen parallel to the plate. A reference laser has wavelength $600\ \mathrm{nm}$ With the original plate and a screen distance of $1.20\ \mathrm{m}$ the measured fringe separation is $3.00\ \mathrm{mm}$

(a)

Show that the slit separation of the original plate is approximately $0.240\ \mathrm{mm}$

[2]

(b)

The screen is moved to a distance of $1.80\ \mathrm{m}$ with the original plate and reference laser unchanged. Determine the fringe separation.

[1]

(c)

A replacement plate is used with the reference laser and the screen at $1.80\ \mathrm{m}$ The measured fringe separation is $3.00\ \mathrm{mm}$ Determine the slit separation of the replacement plate.

[1]

(d)

The replacement plate is used with an unknown laser wavelength. The screen is at $1.20\ \mathrm{m}$ and the fringe separation is $2.40\ \mathrm{mm}$ Determine the wavelength of this laser.

[2]

(e)

In a further run, an unknown laser gives a fringe separation of $3.00\ \mathrm{mm}$ with the screen at $1.20\ \mathrm{m}$ but the identity of the slit plate used was not recorded. A technician claims that the laser wavelength is the same as that of the reference laser. Determine whether this claim is justified, supporting your answer quantitatively.

[4]

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