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What happens to the intensity of light f...

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 legth of room, its intesity essentially ramain constant.
What geonetrical characteristric of LASER beam is responsible for the constnat intensity which is missing in the case of light from the bulb?

Text Solution

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Intensity of light is reduced to one fourth because the light beam spreads as it approaches into a spherical
region of area `4pir^2`,i.e., `Iprop1//r^2`. But laser beam dose not spread, hence its intensity remains constant. Laser beam is is unidirectional, monochromatic and coherent light, whereas the light from a bulb does not
possess the above properties.
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