Question

The work function for a metal is 50 eV. To emit photo electrons of zero velocity from the surface of the metal, the wavelength of the incident light should be $xnm$. The value of $x$ is:

• A. $24.8$
• B. 27
• C. 26
• D. 20

Answer 1

The correct option is A $24.8$

Gievn: Work function, $\varphi$ = 50 eV

According to Einstein's photoelectric effect,
Work function, $\varphi =h\nu -K.E$
As the velocity of the emitted photoelectron is zero, the K.E of the photo electron will also be zero.
So, $\varphi =h\nu$
We know, $\text{E (in eV)}=\frac{12400}{\text{wavelength}\left(A^o\right)}$
$\Rightarrow h\nu =\frac{12400}{\text{wavelength}\left(A^o\right)}$
$\Rightarrow \text{wavelength}=\frac{12400}{50}=248A^o=24.8nm$