Question

Assertion : The energy $(E)$ and momentum $(p)$ of a photon are related by $p=E/c$. Reason : The photon behaves like a particle.

• 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)

When an electron/proton behaves like a particle, then its wavelength is given by
$\lambda =\frac{h}{p}$ ...(1)
where $h$ is Planck constant, $p$ is momentum. This wavelength is know as de-Broglie wavelength of the electron. Also
$E=hv=\frac{hc}{\lambda }$ ...(2)
where $v$ is frequency, $c$ is speed of light.
From Eqs. (1) and (2), we get
$p=\frac{E}{c}$