Question

Ultraviolet light by wavelength $200 \, nm$ is incident on the polished surface of $Fe$ (Iron). The work function of the surface is $4.71 \, eV$ . What will be its stopping potential?

$\left(h = 6 .626 \times \left(10\right)^{- 34} \, J \, s ; \, 1 \, eV = 1 .6 \times \left(10\right)^{- 19} \, J ; \, \, C = 3 \times \left(10\right)^{8} \, m \, s^{- 1}\right)$

• A. $1.5V$
• B. $2.5V$
• C. $0.5V$
• D. None of these

Answer 1

Answer: (A)

Stopping potential $\times $ energy = $KE_{m a x}$
$E= \, \phi+kE_{m a x}$
$kE_{m a x}=E- \, \phi$
$=\frac{h C}{200 nm}-4.71 \, eV$
$=6.2 \, eV-4.71 \, eV$
$=1.49 \, eV$ $\sim 1.5eV$
Stopping potential $V=1.5 \, V$