IB Physics HL C 3 12 Hl Single Slit Diffraction Questions

Practise IB Physics HL C.3.12 by solving single-slit diffraction, central-maximum and intensity-distribution problems across wave systems.

Exam points

Calculate single-slit minima from slit width, wavelength and diffraction angle.
Explain how slit width and wavelength change the central maximum and diffraction spread.
Interpret single-slit intensity graphs and justify diffraction behaviour for sound, light or radio waves.

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Study C.3.12 (HL)—Single-slit diffraction conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[Maximum number: 2]

A student investigates how light can be used to measure the speed of a toy train.

$Figure for Question IB Physics HL C 3 12 Hl Single Slit Diffraction Questions question 1 — IB Physics HL$

Light from a laser is incident on a double slit. The light from the slits is detected by a light sensor attached to the train.

The graph shows the variation with time of the output voltage from the light sensor as the train moves parallel to the slits. The output voltage is proportional to the intensity of light incident on the sensor.

$Figure for Question IB Physics HL C 3 12 Hl Single Slit Diffraction Questions question 1 — IB Physics HL$

As the train continues to move, the first diffraction minimum is observed when the light sensor is at a distance of 0.13 m from the centre of the fringe pattern.

$Figure for Question IB Physics HL C 3 12 Hl Single Slit Diffraction Questions question 1 — IB Physics HL$

(not to scale)

Determine the width of one of the slits.

angular width of diffraction minimum $=\frac{0.13}{5.0}=0.026\ \mathrm{rad}$

slit width $=\frac{\lambda}{d}=\frac{6.3\times10^{-7}}{0.026}=2.4\times10^{-5}\ \mathrm{m}$

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