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?

Given,


Time taken by laser to reflect back from moon to earth = 2.56 s


We know that,


Speed of the light in vacuum = 3×108 m/s


Radius of the lunar orbit (r) = distance between Earth and Moon (d)


Times taken for laser beam to reach moon = 0.5×2.56 = 1.28 s


∴ r = d = speed of light in vacuum × Time taken


= 3×108 × 1.28 m


= 3.84×105 km


Hence, the radius of the lunar orbit is, 3.84×105 km.


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