Question

The intensity of light bulb measured in watts per square meter (w/m^2), varies inversely as the square of the distance d from the light bulb. suppose is 45 w/m^2 when the distance is 5 m. find the intensity when the distance from the light bulb is 7 m away

Answer 1

I(7) = 22.96 W/m²

Explanation:

Let intensity of light, be I(d) where d is distance. There must be a proportionality factor K such as

I(d) = K /d²

Now for d = 5 m I(d) = K* 1/d²

then 45 * 25 = K

K = 1125

To find the intensity when the distance from the light bulb is 7 m away

I(7) = K / 49

I(7) = 1125/49 W/m²

I(7) = 22.96 W/m²