Question

The work function of a metal $2.8eV$. Its threshold wavelength will be :

• A. $4400\mathring{A}$
• B. $4433\mathring{A}$
• C. $5434\mathring{A}$
• D. $433\mathring{A}$

Answer 1

Answer: (B)

The work function $(W)$ is the minimum energy needed to remove an electron from a solid to a point immediately outside the solid surface.
It is given by $W=\frac{hc}{\lambda }$ where $h$ is Plancks constant, $c$ the speed of light and $\lambda$ the threshold wavelength.
Given, $W=2.8eV=2.8\times 1.6\times 10^{-19}J$
$h=6.6\times 10^{-34}J-s,c=3\times 10^{8}m/s$
$\lambda =\frac{6.6\times 10^{-34}\times 3\times 10^8}{2.8\times 1.6\times 10^{-19}}$
$\lambda =4433\times 10^{-10}m$
$\Rightarrow \lambda =4433\mathring{A}$