A moving hydrogen atom absorbs a photon of wavelength 221 nm and stops. If the mass of the hydrogen atom is \( 1.67 \times 10^{-27}\,\mathrm{kg} \), what will be the linear momentum of the photon? (Given: \( h = 6.63 \times 10^{-34}\,\mathrm{J\,s} \))
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( 3 \times 10^{-27}\,\mathrm{N\,s} \)
The momentum of a photon depends only on its wavelength, through the de Broglie relation, so the mass of the atom is not needed.
\( \displaystyle p = \frac{h}{\lambda} \)
\( \lambda = 221\,\mathrm{nm} = 221\times10^{-9}\,\mathrm{m} \)
\( \displaystyle p = \frac{6.63\times10^{-34}}{221\times10^{-9}} = 3.0\times10^{-27}\,\mathrm{N\,s} \)