Question

Which of the following was one of the two basic postulates of special relativity formulated by Albert Einstein?
A. Accelerating reference frames are equivalent to non – accelerating reference frames
B. The speed of light does not change in all inertial reference frames.
C. Speed of photons is more than the speed of light waves.
D. Mass is converted completely into energy when moving at the speed of light.
E. Physical laws are relative.

Answer 1

We are given some statements and are asked to find which of them is a postulate of special relativity. Special theory of relativity is a theory that gives us the relation between space and time. The theory consists of two basic postulates.

Complete step by step answer:
In the question we are given five statements and we are asked which one of them is a postulate of Einstein’s special theory of relativity.
The first basic postulate of Einstein’s special theory of relativity is about the reference frames. And the second postulate of special relativity deals with the speed of light.
In the question the given options are about the speed of light. Hence let us look into the second postulate of the theory.
By the laws of electricity and magnetism it was predicted that the speed of light in vacuum is $3\times {{10}^{8}}m/s$. But it was not specified about the frame of reference in which the light is.
But, Einstein by his second postulate in his special theory of relativity stated that the speed of light is a constant independent of the relative motion of the source, i.e. the speed of light will be constant in all the inertial frames of reference.

So, the correct answer is “Option B”.

Note: In the first postulate it is said that the laws of physics are invariant, or we can say that the physical laws will remain the same and can be stated in their simplest form in all inertial frames of references.
Inertial frame of reference is simply a reference frame where an object at rest will continue to be in rest, or an object in motion will continue to be in motion until external force is acted on them.