Question

What happens to the intensity of light from a bulb if the distance from the bulb is doubled? As a laser beam travels across the length of a room, its intensity essentially remains constant.What geomatrical characteristic of LASER beam is responsible for the constant intensity which is missing in the case of light from the bulb?

Answer 1

Intensity is reduced to one fourth. T is beacause the light beam spreads, as it propogates into a spherical region of area 4πr², but LASER does not spread and hence its intensity remains constant.