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 a laser light beamed at the Moon to return back to earth is 2.56 s.

Distance between earth and moon is given as,

D=c× t 2

Where, t is the time taken by light to travel to the Moon and back to the earth and c is the speed of light.

By substituting the given values in the above formula, we get

D=3× 10 8 × 2.56 2 =3.84× 10 8  m =3.84× 10 5  km

Radius of the lunar orbit is equal to the distance between earth and moon.

Thus, the radius of lunar orbit is 3.84× 10 5  km.