Question

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

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

Answer 1

The correct option is A $1.6\times {10}^{15}Hz$

Energy released from emission of electron

$E=10.2eV$

From photo electric equation work function,

$\varphi =E-eV=hv$

$v=\frac{E-eV}{h}$

$=\frac{(10.2-3.57)e}{6.67\times {10}^{-34}}$

$=\frac{6.63\times 1.6\times {10}^{-19}}{6.67\times {10}^{-34}}=1.6\times {10}^{15}Hz$