Units and Measurement

Question : 29

Total: 33

A laser is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon’s surface. How much is the radius of the lunar orbit around the Earth?

Solution:

Here, t=2.56 s
velocity of laser light in vacuum, c=3×108m∕s
The radius of lunar orbit is the distance of moon from earth. Let it be x
As x=

c×t

∴ x=

3×108×2.56

=3.84×108 m

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