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?

We known that speed of laser light = c = 3 x 10m/s. If d be the distance of Moon from the earth, the time taken by laser signal to return after reflection at the Moon’s surface
Then,
t=2.56 =2dc
d=12×2.56×3×108=3.84×108 m