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

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 Topic Practice

Question 1