An electron of a stationary hydrogen atom passes from the fifth energy level to the ground level. The velocity that the atom acquired as a result of photon emission will be: (m is the mass of electron, R, Rydberg constant and h Planck’s constant)

Options

(a) 24hR / 25m
(b) 25hR / 24m
(c) 25m / 24hR
(d) 24m / 25hR

Correct Answer:

24hR / 25m

Explanation:

For emission, the wave no. of the radiation is given as
1/λ = Rz² (1/n₁² – 1/n₂²)
R = Rydberg constant, Z = atomic number
= R (1/1² – 1/5²) = R (1 – 1/25) ⇒ 1/λ = R 24/25
linear momentum
P = h/λ = h x R x 24/25 (de-Broglie hypothesis)
⇒ mv = 24hR / 25 ⇒ V = 24hR / 25m