Question

Ii. Two lamps are hung at a height of 6m from ground. The distance between the lamps is 8m, one

lamp is of 500c.p. Find the candle power (C.P) of the second lamp if the illumination just below the
first lamp is 20 lux.

Answer 1

The illumination just below the first lamp can be calculated using the inverse square law, which states that the intensity of light decreases with the square of the distance from the source. The formula for the illumination (I) at a distance (d) from a point source with candle power (C.P) is:

I = (C.P / 4πd²) lux

In this case, we can use the illumination just below the first lamp to find the C.P of the second lamp. We know that the distance between the lamps is 8m, so the distance from the first lamp to the ground directly below it is 6m. Using the inverse square law, we can find the C.P of the first lamp as follows:

20 lux = (500 C.P / 4π(6m)²)

20 lux = (500 C.P / 452.39)

C.P = (20 lux x 452.39) / 500

C.P = 18.14

Therefore, the candle power of the second lamp should also be 18.14 C.P in order to achieve the same illumination just below it.