Measurement of Light Intensity Using a Light Dependent Resistor


Retort stand/clamp/boss, metre ruler, mounted LDR, 12V light bulb, power supply for the light bulb, multimeter used as an ohmmeter, connecting wires.


A student suggests that the difference in resistance,of a LDR (light-dependent-resistor), when a light source is switched on and off, will be inversely proportional to the square of its distance away from a light source; i.e.

The student uses the following argument to support the above hypothesis:

The intensity,of light from a source is inversely proportional to the square of the distance from the source; i.e.

The student then states that the change in resistance,of an LDR is proportional to the change in intensity of light falling on it i.e.

Combining these two relationships results in the claim that


Use the apparatus supplied to test out the student's hypothesis.

Your write up should include:

(a) a simple diagram showing how you used the apparatus

(b) a table of results and / or a relevant graph

(c) a clear explanation of how you used your results to confirm or refute the hypothesis that

(d) an account of any precautions you took in order to obtain good results.

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