Question

Photons of energy 12.1 eV can excite hydrogen atoms. Find the maximum wavelength of the radiations emitted when electrons drop back to ground state –

• A. 6563 Å
• B. 1026 Å
• C. 1215 Å
• D. 9567 Å

Answer 1

Answer: (A)

6563 Å

Answer 2

Energy required by an electron to jump to

n = 3 level = 13.6 – 1.5 = 12.1 eV

Electron in n = 3 level an return to ground level in following ways

(i) n = 3 to n = 2 and then n = 2 to n = 1

(ii) n = 3 to n = 1

from n = 3 to n = 2

$\frac{1}{\lambda} = R\left( \frac{1}{2^{2}} - \frac{1}{3^{2}} \right)$ Ž l = 6563 Å

from n = 2 to n = 1

$\frac{1}{\lambda} = R\left\lbrack \frac{1}{1^{2}} - \frac{1}{2^{2}} \right\rbrack$ Ž l = 1215 Å

from n = 3 to n = 1

$\frac{1}{\lambda} = R\left\lbrack \frac{1}{1^{2}} - \frac{1}{3^{2}} \right\rbrack$ Ž l = 1026 Å