Question

The intensity I of light (measured in foot-candles) varies inversely with the square of the distance from the bulb. Suppose the intensity of a 100-watt light bulb at a distance of 2 meters is 0.075 foot-candle. Determine the intensity of the bulb at a distance of 3 meters.

Answer #1

Here, it is given that the Intensity 'I' of light is inversely proportional to the square of the distance from the bulb

Or

or , where k is a constant

It is given that when distance is 2 meters away ,intensity is 0.075 foot candle

Substituting in the equation, we get

We need to find the intensity when the distance is 3 meters away.

Substituting the necessary variables, we get

**Intensity is 0.0333334 foot candles at a distance of 3
meters away from the light bulb**

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