Question

Let $E$ and $p$ be energy & momentum of a photon. If the frequency is increased,

• A.
  Both $p$ & $E$ will decrease
• B.
  $E$ increase, $p$ decreases
• C.
  Both $p$ & $E$ will increase
• D.
  $p$ increases, $E$ decreases

Answer 1

The correct option is C

Both $p$ & $E$ will increase
Using $p=\frac{h}{\lambda },E=h\nu =\frac{hc}{\lambda }$

$\Rightarrow p=\frac{E}{c}$

$\therefore$ both $p$ & $E$ will increase as frequency is increased.

Hence, $\left(C\right)$ is the correct answer.

$\begin{array}{c}\text{Key Concept :-}E=pCE\propto p\\ \text{Therefore energy is directly propotional}\\ \text{to momentum. This formula is applicable}\\ \text{only for light rays.}\\ \text{For particles}E=\frac{p^2}{2m}\text{(Ignoring relativistic effect))}\end{array}$