Question

The work function of a surface of a photosensitive material is 6.2 eV. The wave length of incident radiation for which the stopping potential is 5V lies in the

• A. Ultraviolet region
• B. visible region
• C. infrared region
• D. X - ray region

Answer 1

The correct option is A Ultraviolet region

Work function of the surface $\varphi =6.2eV$
Stopping potential $V_o=5V$
Thus energy of the incident radiation $E=e{V}_o+\varphi =5+6.2=11.2eV$
Wavelength of the radiation $\lambda =\frac{1240}{E\left(ineV\right)}nm$
$⟹\lambda =\frac{1240}{11.2}=110.7nm$
Wavelength of ultraviolet ranges from 100 nm to 400 nm.
Thus the wavelngth of incident radiation lies in ultraviolet region.