Modern Physics 1 Question 7

6. Radiation coming from transitions n=2 to n=1 of hydrogen atoms fall on He+ions in n=1 and n=2 states. The possible transition of helium ions as they absorb energy from the radiation is

(Main 2019, 8 April I)

(a) n=2n=3

(b) n=1n=4

(c) n=2n=5

(d) n=2n=4

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Solution:

  1. De-excitation energy of hydrogen electron in transition n=2 to n=1 is

E=13.6×1nf21ni2eV=13.6112122=10.2eV

Now, energy levels of helium ion’s (He+)electron are (For helium, Z=2 )

n=46.04eV10.2eVn=313.6eVn=254.4eV

So, a photon of energy 10.2eV can cause a transition n=2 to n=4 in a He+ion.

Alternate Solution

For He+ion, when in n=1 state,

$$



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