Question

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

• A. 2.75 m/s
• B. 3.25 m/s
• C. 4.85 m/s
• D. 5.65 m/s

Answer 1

Answer: (B)

3.25 m/s

Answer 2

Linear momenta of photon and electron are equal and opposite.

p = mv = $\frac{h}{\lambda}$

v = $\frac{h}{m\lambda}$= $\frac{6.62 \times 10^{–34}}{1.67 \times 10^{–27} \times 122 \times 10^{–9}}$

v = 3.25 m/s