Question

The distance between the bulb and the point vertical below it is 2m, if the distanc is increased by 1m, then illuminance is decreased by??

Answer 1

Illuminance is decreased by `55.55%`.

Explanation:

Illuminance is inversely proportional to the square of the distance.

As distance increases from `2` meters to `3` meters

illuminance reduces by `2^2/3^2=4/9`

i.e. if it is `1` unit at a distance of `2` meters, at a distance of `3` units it is nly `4/9` units

and reduction is `5/9:1` or `5/9xx100%=55.55%`

Hence illuminance is decreased by `55.55%`.