question_answer 40)

    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:

                    Intensity of light is reduced to one fourth because the light beam spreads as it approaches into a spherical region of area. But laser beam does not spread, hence its intensity remains constant.  Laser beam is unidirectional, monochromatic and coherent light, whereas the light from a bulb does not possess the above properties.