Question

The work function of sodium is 2.3 eV. The threshold wavelength of sodium will be

• A. $2900\stackrel{o}{A}$
• B. $\text{2500 }\stackrel{o}{A}$
• C. $\text{5380 }\stackrel{o}{A}$
• D. $\text{1200 }\stackrel{o}{A}$

Answer 1

Answer: (C)

Here, work function $W_0=2.3eV=2.3\times 1.6\times {10}^{-19}J$ where, ${\lambda }_0$ is the threshold wavelength for sodium. Then, $W_0=\frac{hc}{{\lambda }_0}$ or ${\lambda }_0=\frac{hc}{W_0}$ ${\lambda }_0=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{2.3\times 1.6\times {10}^{-19}}$ $=5380\times {10}^{-10}m$ $=5380\stackrel{o}{A}$