Light dependent resistors

The resistance of an LDR reduces with the intensity of light falling on it. This can be measured using the SEN terminal.

Objective

Learn about LDR. Measure intensity of light and its variation with distance from the source.

Procedure

Connect the LDR from SEN to ground
Connect a wire from SEN to A1
Measure the LDR’s resistance, for different light intensities.
Iluminate LDR using a fluorescent lamp, A1 should show ripples
Set the time base to 200mS full scale
Put A1 in AC mode, using the switch, and measure ripple frequency

Discussion

The resistance vary from 1kΩ to around 100 kΩ depending on the intensity of light falling on it. The voltage is proportional to the resistance. The resistance decreases with intensity of light. If you use a point source of light, the resistance should increase as the square of the distance between the LDR and the light source. The light from a fluorescent lamp operating at 50Hz has 100Hz ripples and these can be measured.