Question

In photoelectric effect, the threshold wavelength of sodium is $5000 \, $ . Find its work function $\left(\right.h=6.6\times \left(10\right)^{- 34} \, J s, \, c=3\times \left(10\right)^{8} \, \left(m \, s\right)^{- 1}, \, 1 \, eV=1.6\times \left(10\right)^{- 19} \, J\left.\right)$

• A. $7.5 \, \text{eV}$
• B. $2.5 \, \text{eV}$
• C. $10 \, \text{eV}$
• D. $5.0 \, \text{eV}$

Answer 1

Answer: (B)

The work function of sodium
$W = \frac{h c}{\lambda _{0}}$
$W=\frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{5 \times 10^{- 7}}$
or $ \, W=3.96\times 10^{- 19} \, J$
or $W=2.5 \, eV \, \, $