IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

# Variation of Light Intensity with Distance!

## Procedure

This was demonstrated by Ms Smita Fangaria at Kolkata SRP. Take two bulbs, of different power, say 60 watt and 100 watt. Take sheet of paper. Apply some oil/butter at a spot. This spot becomes translucent. Put two bulbs at some distance, say 1 metre. Move the paper between two sources till intensity on opaque and translucent part of the paper looks same. Measure the distance. See whether $$I\propto\frac{1}{r^2}$$.

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