IB Physics HL C.3.13 Diffraction Envelope Question Bank
Practise IB Physics HL C.3.13 by analysing how a finite-slit diffraction envelope modulates double-slit interference maxima.
- Syllabus
- First assessment 2025
- Course
- Physics HL
- Level
- HL
Practise IB Physics HL C.3.13 by analysing how a finite-slit diffraction envelope modulates double-slit interference maxima.
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.

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.

(not to scale)
Suggest the variation in the output voltage from the light sensor that will be observed as the train moves beyond the first diffraction minimum.
«beyond the first diffraction minimum» average voltage is smaller
«voltage minimum» spacing is «approximately» same OR
rate of variation of voltage is unchanged
OWTTE