Question

If a surface has work function of 3.00 eV, the longest wavelength of light which will cause the emission of electrons is

• A. $4.8\times {10}^{-7}m$
• B. $5.99\times {10}^{-7}m$
• C. $4.13\times {10}^{-7}m$
• D. $6.84\times {10}^{-7}m$

Answer 1

Answer: (C)

$4.13\times {10}^{-7}m$

Here the threshold wavelength is the longest wavelength of light which will cause the emission of electrons.

We know that work function, $W=\frac{hc}{{\lambda }_0}$

or ${\lambda }_0=\frac{hc}{W}=\frac{(6.62\times {10}^{-34})\times (3\times {10}^8)}{3\times 1.6\times {10}^{-19}}=4.13\times {10}^{-7}m$