If h is Planck’s constant, the momentum of a photon of wavelength 0.01 Å is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( 10^{12}\,h\,\mathrm{m^{-1}} \)
A photon of frequency \( \nu \) carries momentum \( p=h\nu/c \). Since \( c=\nu\lambda \), this is \( p=h/\lambda \), so the momentum follows directly from the wavelength.
Since 1 Å = \( 10^{-10}\,\mathrm{m} \), the wavelength in metres is:
\( \begin{aligned} \lambda &= 0.01\times10^{-10}\,\mathrm{m} \\ &= 10^{-12}\,\mathrm{m} \end{aligned} \)
\( \begin{aligned} p &= \frac{h}{\lambda} \\ &= \frac{h}{10^{-12}\,\mathrm{m}} \\ &= 10^{12}\,h\,\mathrm{m^{-1}} \end{aligned} \)