Question

How are lasers used to determine the distance from earth to the moon?

Answer 1

A beam of laser is directed at a reflecting surface put on the moon when the beam of laser is reflected a receiver on the each measure the time since the beam was sent till it was received. Laser is simply light so it has constant velocity in vacuum ~ air  (c = 3 x 10^8 m/s)

to find the distance:

t : time measured between launching the beam and receiving it 

d : distance

d = ct 

Answer 2

Explanation :

Lasers are used to determine the distance from earth to the moon. It is known as the Lunar Laser Ranging experiment. Laser is nothing but a a light source.

This can be done by passing a flash of light towards the moon. A reflector is placed on the surface of moon by the members of Apollo mission. With the help of this reflector light is reflected back to the earth.

The time taken by the light to travel the surface of moon and back to earth is calculated. It was approximately 2.55 seconds. So, for one side time is 1.275 seconds.

We know that the speed of light is c i.e. $3\times 10^8\ m/s$.

Distance from Earth to the Moon is, d = c t

So, $d=3\times 10^8\ m/s \times 1.275\ s$

$d=3.825\times 10^8\ m$

$d=382500\ Km$

Hence, this is the required solution.