A milliwatt laser is said to be more intense than a 40 watt bulb. Explain

Asked by  | 21st Mar, 2009, 11:15: AM

Expert Answer:

A laser beam is more intense because all the emitted waves are in phase or coherent.

In a light bulb the waves are out of phase or incoherent. In this case the resultant intensity would be the sum of the individual intensities and this is proportional to n x a2. Here n is the number of waves and a is the amplitude of each wave.

But the intensity of a laser will be proportional to n2a2. This is true as the waves are in phase with each other so their total amplitude is na.

So the intensity is greater by a factor of n. Since n is very large, the laser will be very intense as compared to a light bulb.

Answered by  | 6th Apr, 2009, 10:33: AM

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