00:01
Hello, in the question we have given that during apollo 11 moon landing a retro -reflecting panel was erected on moon surface.
00:12
So, the speed of light can be found by measuring the time it takes a laser beam to travel from earth, reflect from the panel and return.
00:21
So see, if this is the moon surface, so if say this is the surface of the moon, so the retro -reflecting panel is set up over here on the moon surface and the laser beam, so a laser beam is sent from here.
00:42
So, this will go, it will hit the reflector and it will come back.
00:49
So, now the time taken, so time taken to travel this beam is measured and then we have to find out the speed of light.
01:02
So, they have mentioned that this time interval is equal to 2 .51 seconds.
01:08
So, it takes 2 .51 seconds to reflect from the panel and return to the earth.
01:17
So, we have to, what is measured speed of light? so, take center to center distance.
01:25
So, the center to center distance from earth to moon is given that is 3 .84 into 10 raised to 8 meters.
01:37
But now this, this setup is on the surface.
01:42
So, the laser beam is directed from the surface and on this moon, this reflector is also set up on the surface of the moon.
01:52
So, we need the surface to surface distance.
01:55
So, in order to get the surface to surface distance, we should know the radius of earth.
02:03
So, radius of earth is 6380 kilometers and radius of moon is equal to 1740 kilometers.
02:14
So, surface to surface distance, so surface to surface distance between the earth and moon is, let us call it as small r.
02:34
So, that will be equal to this center to center distance minus this radius of earth minus radius of moon.
02:45
And then we get the surface to surface distance...