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 distance. 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 ?

Explanation

Time taken by LASER beam to come back to Earth after reflection from Moon surface T = 2.56 s
`:.` Time taken by LASER beam to reach to Moon
`t=(T)/(2)=(2.56)/(2)=1.28s`
Speed of LASER beam (Speed of light)
`c=3xx10^(8)ms^(-1)`
Distance of Moon from Earth D=ct
`=3xx10^(8)xx1.28`
`=3.84xx10^(8)m`
`=3.84xx10^(5)km`
The radius of the lunar of orbit around the Earth is `3.84xx10^(5)` km.