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 geometrical characteristic of LASER beam is responsible for the constant intensity which is missing in the case of light from the bulb?

Question

Philoid · Accepted Answer

The intensity of the light from the point source is given by,

Where,

r= Distance from the source

Now if the distance id doubled the intensity becomes one fourth times the original value.

For laser source the beam does not spread, so the intensity remains the same.

The characteristic of laser which causes the constant intensity and missing in the bulb are as follows,

 Monochromaticity

 Unidirectionality

 Coherent nature of light

 Highly collimated beam