Question

An electron jumps from seconds excited state of hydrogen atom to its ground state and the photon thus emitted is incident on a photo sensitive metal plate of work function 5.1 eV .The stopping potential for the plate would be (approximately)

• A. 4 V
• B. 3 V
• C. 7 V
• D. 9 V

Answer 1

The correct option is B 3 V

$E=K.E_{max}+w$

$=e{v}_o+w$

$=10+2=75$

$E=12.75eV$

The difference of $4$ and $1$ energy level is $12.75$eV so the higher energy level is $4$ to ground and excited state.

$\therefore n=3$.