IB Physics HL C 3 9 Young Double Slit Equation Questions

Practise IB Physics HL C.3.9 by solving Young double-slit equation problems with fringe spacing, angular separation and changing geometry.

Exam points

Solve multi-step s = λD/d problems and determine how changing D, d or λ changes fringe spacing.
Use angular separation and fringe measurements to infer wavelength or slit separation with consistent units.
Analyse experimental graphs and geometry when calculating wavelength from double-slit data.

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Study C.3.9—Young double-slit equation conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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

Figure for Question IB Physics HL C 3 9 Young Double Slit Equation 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.

The slits are separated by 1.5 mm and the laser light has a wavelength of $6.3 \times 10^{-7} \mathrm{~m}$ . The slits are 5.0 m from the train track. Calculate the separation between two adjacent positions of the train when the output voltage is at a maximum.

$s=\frac{\lambda D}{d}=\frac{6.3\times10^{-7}\times5.0}{1.5\times10^{-3}}=2.1\times10^{-3}\ \mathrm{m}$

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IB Physics HL C 3 9 Young Double Slit Equation Questions question 1