Question

Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be $3.57\, V.$ The threshold frequency of the material is

• A. $4 \times 10^{15} Hz$
• B. $5 \times 10^{15} Hz$
• C. $1.6 \times 10^{15} Hz$
• D. $2.5 \times 10^{15} Hz$

Answer 1

Answer: (C)

$1.6 \times 10^{15} Hz$

Answer 2

Energy released from emmition of electron is $E =(-3.4)-(-13.6)=10.2\, eV$. From photo-electric equation, work function $\phi= E - eV _{0}= h v _{0}$ On Solving this $v_{0}=1.6 \times 10^{15}\, Hz$