Question

Out of the following, whose velocity is equal to that of light?
A. of $\beta $rays.
B. of sound waves
C. of ultrasonic waves
D. none of these.

Answer 1

Hint: As a very first step, you could read the question well along with all the given options. Then you could recall what is the significance of velocity of light c and also all the related properties of c. You could then recall the ones that have this velocity when they propagate and thus check for the given ones in them.

Complete step by step answer:
In the question, we are given few options and we are supposed to find the one that has its velocity equal to that of light. Before going to the solution of this question, let us define the velocity of light and its significance.
We normally denote the speed of light vacuum by c and it is considered as a universal physical constant and this constant has great significance in many areas of physics. The value is found to be $c=3\times {{10}^{8}}m{{s}^{-1}}$
Though we normally associate this speed to that associated with light, we can also say that all massless particles and field perturbations travel in vacuum with this speed and also all the EM waves and gravitational waves.
Therefore, we find that none of the above mentioned ones fall to the mentioned categories

So, the correct answer is “Option D”.

Note: Under the concept of special relativity, c is considered to be the upper most limit for velocity that can be exhibited by any conventional matter, energy or any signal that is known to carry information through space. Point to be noted is that light does have different velocity in different mediums, c is exclusively for vacuum.