Answer to Question #164238 in Quantum Mechanics for Plasmother

Question

Describe one method by which the speed of light can be measured, explaining how the result is calculated from the observations. Describe one practical situation in which a knowledge of the speed

       of light, or other electromagnetic radiation is needed.

Answer 1

Answer

According to physics concept

The speed of light was measured using the Foucault method of reflecting a beam of light from a rotating mirror to a fixed mirror and back creating two separate reflected beams with an angular displacement that is related to the time that was required for the light beam to travel a given distance to the fixed mirror.

Foucault devised a method which was able to avoid such issues by 

indirectly measuring the time the light traveled.

Diagram is given as

Foucault’s method used a light source and rotating mirror 

together to derive the speed of light2. The Foucault method uses the light source to produce a focused beam 

on the rotating mirror. The light from the rotating mirror is then reflected at an angle to a fixed mirror 

which is aligned to face perpendicular to the reflected light beam. Therefore the light is reflected directly

back to the rotating mirror where it was first reflected. During the time the light had traveled the distance 

between the two mirrors, the rotating mirror had changed its orientation to the beam of light,

Speed of light is given

$c=\frac{D}{t}$