In this activity students explore how the number of tracing paper sheets changes the amount of light that is transmitted.
Each students will need:
- A smartphone with phyphox installed
- A light source
- 10 sheets of tracing paper (large enough to cover the phone camera)
Close blinds or curtains and turn off any background light sources to ensure you are in a dark room.
Consider pairing or grouping students to ensure each student has access to a device with the light sensor. This can be checked in the phyphox app (if it doesn’t have a light sensor, “light” will be greyed out).
Ask students to:
- Open the phyphox app on their phone, select ‘light’ and select ‘simple’.
- Identify whether the app is gathering data from the front or back camera on their phone by each camera respectively while the app is taking readings. The experiment will be easier to perform if the front camera is taking readings.
- Place their phone face up on a table and set up the bright light source above their phone.
- Press the play button, let the illuminance reading settle and record their reading for 0 sheets of paper (the background light level).
- Place a sheet of tracing paper on top of the phone, covering the light sensor but leaving the display visible, and record the reading for 1 sheet.
- Repeat as 9 more sheets are added.
- Plot a graph of illuminance vs number of sheets.
Students will have seen that light can pass through some materials and recognise from everyday experiences that more translucent materials will let more light pass through. This activity allows them explore transmission in an experimental context.
Typical results are shown below:
As an extension activity, you could ask the students to plot illuminance vs distance using the same set-up, but the students now measure the light level at increasing distances. It is also possible to repeat the experiment for other papers (tissue) or even transparent/translucent materials such as coloured plastic film.
Students describe how the amount of light transmitted by a material depends on thickness.