Question

Assertion: A photon has no rest mass, yet it carries definite momentum.
Reason: Momemtum of photon is due to its energy and hence its equivalent mass.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (A)

Equivalent mass of photon (m) is given from equation
$E=mc^{2}=h\upsilon $
$\therefore m=\frac{h\upsilon}{c^{2}}$
Where $E$ is energy, $m$ is mass, $c$ is speed of light, $h$ is Planck’s constant, $u$ is frequency.
$\therefore $ Momentum of photon $=\frac{h\upsilon}{c^{2}}\times c=\frac{h\upsilon}{c}$