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  4. A hydrogen atom moving at a speed v absorbs a photon of wavelength 122 nm and stops. The value of v is -

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Q. A hydrogen atom moving at a speed $v$ absorbs a photon of wavelength $122 \, nm$ and stops. The value of $v$ is -

NTA AbhyasNTA Abhyas 2022

Solution:

Linear momentum of photon and electron are equal and opposite
$p=mv=\frac{h}{\lambda }$ , where $m,v,h\&\lambda $ represents mass, velocity, Plank's constant and wavelength respectively.
$v \, =\frac{h}{m \lambda }=\frac{6.62 \times 1 0^{- 34}}{1.67 \times 1 0^{- 27} \times 122 \times 1 0^{- 9}}$
$v \, = \, 3.25 \, m / s$