Investigating LDR’s

Investigating LDR’s


  • LDR
  • multi-meter
  • desk lamp
  • metre rule


In this investigation the dependent variable is the resistance of the LDR, the independent variable is the light intensity which changes as the lamp is moved to different distances.

To make this a fair test the same lamp must be used throughout the experiment. The ambient light (the light in the room from outside or overhead lights) should also be kept constant.


  1. Connect the LDR to the multi-meter and select the resistance setting.
  2. Using the metre rule position the lamp on the desk at a distance of 10 cm from the LDR.
  3. Switch on the lamp and using the meter measure the resistance of the LDR.
  4. Repeat this at distances of 20, 30, 40 and 50 cm.

Risk Assessment

The light bulb will get hot and could cause a burn, to prevent this switch the lamp off when it not being used and avoid touching the bulb. The bulb is also made of glass and could easily be broken, broken glass could cause cuts so report breakages immediately and handle the lamps with care. Electrical items in contact with water could result in an electric shock, make sure that the area you are working in is dry and not too close to the sinks in the lab.


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