Search any question & find its solution
Question:
Answered & Verified by Expert
Assertion: The relative velocity of two photons travelling in opposite direction is the velocity of light.
Reason : The rest mass of photon is zero.
Options:
Reason : The rest mass of photon is zero.
Solution:
2989 Upvotes
Verified Answer
The correct answer is:
If both assertion and reason are true but reason is not the correct explanation of assertion.
Velocity of first photon $=u=c$
Velocity of second photon $=v=-c$
Now, relative velocity of first photon with respect to second photon
$=\frac{u-v}{1-\frac{u v}{c^2}}=\frac{c-(-c)}{1-\frac{(c)(-c)}{c^2}}=\frac{2 c}{1+\frac{c^2}{c^2}}=\frac{2 c}{1+1}=\frac{2 c}{2}=c$
Also the rest mass of photon is zero.
Velocity of second photon $=v=-c$
Now, relative velocity of first photon with respect to second photon
$=\frac{u-v}{1-\frac{u v}{c^2}}=\frac{c-(-c)}{1-\frac{(c)(-c)}{c^2}}=\frac{2 c}{1+\frac{c^2}{c^2}}=\frac{2 c}{1+1}=\frac{2 c}{2}=c$
Also the rest mass of photon is zero.
Looking for more such questions to practice?
Download the MARKS App - The ultimate prep app for IIT JEE & NEET with chapter-wise PYQs, revision notes, formula sheets, custom tests & much more.