Question

Activity 25-2. The postulates of special relativity [Accompanies Section 25-4]

Rank the following speeds as measured by you, from fastest to slowest. In each case assume that you are in the vacuum of space. If the speed is the same in any two situations, state this. Explain how you made your ranking.

(i) The speed of a beam of light emitted from a stationary flashlight that is pointed toward you

(ii) The speed of a beam of light emitted from a flashlight that is pointed toward you and is moving toward you at 0.500c

(iii) The speed of a beam of light emitted from a flashlight that is pointed toward you and is moving away from you at 0.500c

(iv) The speed of a beam of light emitted from a flashlight that is pointed toward you and is moving perpendicular to your line of sight at 0.500c

(v) The speed of a beam of light emitted by a flashlight that is pointed toward you; the flashlight is stationary, and you are moving toward the flashlight at 0.300c

Answer 1

The second postulate of special theory of relativity is given below-

"As measured in any inertial frame of reference, light is always propagated in empty space with a definite velocity c that is independent of the state of motion of the emitting body. Or: the speed of light in free space has the same value c in all inertial frames of reference."

So we see that the velocity of beam of light in each cases will be the same.

So there will be no ranking, in each case the beam of light will have same speed.