Question

A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. The number of spectral lines emitted will be

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

The Correct Option is C

According to Bohr's postulates, an electron makes a jump to higher energy orbital if it absorbs a photon of energy equal to the difference between the energies of an excited state and the ground state. Assuming that the collided electron takes energy equal to 10.2 eV or 12.09 eV from the incoming electron beam (some part lost due to collision), the maximum excited state is \( n = 3 \). The number of spectral lines is given by: \[ \frac{3(3 - 1)}{2} = 3. \] Thus, the number of spectral lines emitted is 3.