Question

When a hydrogen atom emits a photon in going transition from n = 5 to n = 1, its recoil speed is almost –

• A. 10^–4 m/s
• B. 2 × 10^–2 m/s
• C. 4 m/s
• D. 8 × 10² m/s

Answer 1

Answer: (C)

4 m/s

Answer 2

$\frac{1}{\lambda} = R\left\lbrack 1 - \frac{1}{25} \right\rbrack = \frac{24R}{25}$

\ P = $\frac{h}{\lambda} = \frac{24Rh}{25} =$ 6.9 × 10^–27 kg-m/sec.

\ v = $\frac{P}{m}$ = $\frac{6.9 \times 10^{- 27}}{1.6 \times 10^{- 27}}$ ≈ 4 m/ss