Ultraviolet light of wavelength 280 nm is used in an experiment on photoelectric effect with lithium whose work function is 2.5 eV as cathode. The stopping potential is (approximately)

(Take Planck’s constant h and velocity of light c) and hc = 1242 eVnm

1.94 V

The correct answer is option (1) : 1.94 V

$K_{max}=eV_0=\frac{hC}{\lambda}-\phi_0, \begin{matrix}V_0 \to \text{Stopping potential}\\\phi_0 \to \text{Work function }\end{matrix}$

$⇒eV_0=\frac{1242}{280}-2.5⇒eV_0=1.9357eV$

$⇒V_0=1.94\, V$