Question

The work function for a metal is 4 eV . To emit a photo electron of zero velocity from the surface of the metal, the wavelength of incident light should be:

• A. $2700\stackrel{o}{A}$
• B. $1700\stackrel{o}{A}$
• C. $5900\stackrel{o}{A}$
• D. $3100\stackrel{o}{A}$

Answer 1

Answer: (D)

$3100\stackrel{o}{A}$

$hv=h{v}_0+KE$ for zero velocity $KE=0$

$hv=h{v}_0$

$hv=4eV$

$\frac{hc}{\lambda }=4eV$

$\lambda =\frac{h\times c}{4eV}$

$=\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{4\times 1.6\times {10}^{-19}}=3100A^o$

Hence, the correct option is $D$