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

Answer 1

We know intensity of light from a point source I α 1/r², r is the distance from point source.

As the distance is doubled, so the intensity becomes one-fourth the initial value. But in case of laser, it does not spread, so its intensity remain same.

Some geometrical characteristics of LASER beam which are responsible for the constant intensity is

1. Unidirection
2. Monochromatic
3. Coherent light
4. Highly collimated

These characteristics are missing in the case of normal light from the bulb.