Modern Physics 1 Question 2

2. An excited He+ion emits two photons in succession, with wavelengths 108.5nm and 30.4nm, in making a transition to ground state. The quantum number n corresponding to its initial excited state is [for photon of wavelength λ, energy E=1240eVλ( in nm)]

(a) n=4

(b) n=5

(c) n=7

(d) n=6

(Main 2019, 12 April I)

radiation of wavelength λ. When the ion gets de-excited to the ground state in all possible ways (including intermediate emissions), a total of six spectral lines are observed. What is the value of λ ?

(Main 2019, 10 April II) [Take, h=6.63×1034Js;c=3×108ms1 ]

(a) 9.4nm

(b) 12.3nm

(c) 10.8nm

(d) 11.4nm

Show Answer

Solution:

  1. Change in energy in transition from n to m stage is given by (n>m),

En=E0Z2n2

Here, Z=2

ΔEn=+13.6×41m21n2=hcλ

Let it start from n to m and then m to ground.

So, in first case,

$$



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