Question

An electron and a photon have same wavelength. If $p$ is the momentum of electron and $E$ the energy of photon, the magnitude of $p / E$ in SI unit is

• A. $3.0 \times 10^{8}$
• B. $3.33 \times 10^{-9}$
• C. $9.1 \times 10^{-31}$
• D. $6.64 \times 10^{-34}$

Answer 1

Answer: (B)

$\lambda=\frac{h}{p}$ (for electron)
or $p=h / \lambda$
and $ E=\frac{h c}{\lambda}$ (for photon)
$\therefore \frac{p}{E}=\frac{1}{c}=\frac{1}{3 \times 10^{8}}$
$=3.33 \times 10^{-9} \,s\, m ^{-1}$