Question

No photoelectrons are emitted from a metal if the wavelength of light exceeds $6000\stackrel{\circ }{A}$. The work function of the metal is approximately equal to

• A. $3\times {10}^{-16}J$
• B. $3\times {10}^{-19}J$
• C. $3\times {10}^{-20}J$
• D. $3\times {10}^{-22}J$

Answer 1

The correct option is B $3\times {10}^{-19}J$

Cut-off wavelength, ${\lambda }_0=6000\stackrel{\circ }{A}=6\times {10}^{-7}m$
Now, work function, $W_0=\frac{hc}{{\lambda }_0}=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{6\times {10}^{-7}}=3.3\times {10}^{-19}J\approx 3\times {10}^{-19}J$
Hence, the correct choice is (b).