An electric bulb is hanging over a table at a height of 1 m above it. The illuminance on the table directly below the bulb is 40 lux. The illuminance at a point on the table 1 m away from the first point will be about

Question

An electric bulb is hanging over a table at a height of 1 m above it. The illuminance on the table directly below the bulb is 40 lux. The illuminance at a point on the table 1 m away from the first point will be about

Philoid · Accepted Answer

Given:

Distance of bulb from table, PQ = 1 m

Distance of point from table, QR = 1 m

Luminosity, I₀ = 40 lux

Calculation:

The position of the bulb is at the point P and position of the point is at R. As, both the sides of the triangle is 1 m. Thus, given triangle is isosceles triangle and the angle θ = 45⁰.

The length of the side PR is,

The illuminance is given as,

E = 14 lux

So, option B is correct.