Electronic and Photonics 2014
Experiment 4 LDRs (Light Dependent Resistors)
In this experiment we will be investigating the relationship between light intensity and the
output voltage of a voltage divider circuit incorporating a light dependent resistor (LDR).
Equipment:
DC supply (set on 2 V)
22 kΩ resistor
LDR
Connecting block
Multimeter (to measure output voltage, set on 2V DC)
Light source (Light box connected to DC power supply, 10 V DC)
Lux meter (to measure light intensity)
Set up the apparatus as shown below:
Measure the output voltage for a range of light intensities, recording your data in excel. Ensure you
obtain reliable values over a wide range of light intensities.
Light intensity, φ (lux)
Output voltage, Vout (V)
Plot a graph of output voltage against light intensity. Print the data table and graph and paste into
your log book.
1. What does your graph imply about the change to the resistance of an LDR as the light
intensity increases?
2. Calculate the resistance of the LDR for two different light intensities. Show your working.
Conclusion: Summarise your findings, describing the effect of the changing light intensity on the
output voltage.
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