Question

Light strikes a sodium surface, causing photoelectric emission. The stopping potential for the ejected electrons is 5.0 V, and the work function of sodium is 2.2 eV. What is the wavelength of the incident light? __nm.

Answer 1

Let's assume energy falling was E work and function φ = 2.2 eV

So 2.2 eV gone in overcoming work function

So energy left = E-2.2 eV

Now stopping potential = 5V

So potential energy gained will be e$V_0$

= 5 eV

$\Rightarrow E-2.2=5$

$E=7.2eV$

$E=7.2\times 1.6\times {10}^{-19}J$

$\frac{hc}{\gamma }=7.2\times 1.6\times {10}^{-19}$

$\gamma =\frac{(6.6\times {10}^{-34}\times 3\times {10}^8)}{7.2\times 1.6\times {10}^{-19}}$

$=1.727\times {10}^{-7}$ m

$=172nm$