A LASER is a source of very intense, monochromatic and unidirectional beam of light

unitsandmeasurement
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#1

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 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 lunar orbit around the earth ?


#2

Time taken by a laser beam to return after reflection at the moon’s surface (T) = 2.56 s
Time taken by a laser beam to reach the moon
t=T/2 = 2.56 /2 = 1.28 s
Speed of laser beam = Speed of light © = 3 x ${{10}^{8}}$ m/s
Distance of the moon from the earth (D) = c xt
= 3 x${{10}^{8}}$ x 1.28
=3.84 x ${{10}^{8}}$
=3.84 x$ {{10}^{5}}$ km
.’. Radius of lunar orbit around the earth = 3.84 x $ {{10}^{5}}$