Question

Work function of tungsten and sodium are 4.4 eV and 2.3eV respectively. If threshold wave length of sodium is 5460 , then the threshold wavelength of tungsten is

• A. 6000
• B. 2854
• C. 8000
• D. 11300

Answer 1

The correct option is B 2854

Let work function of metal surface be $\varphi$
Threshold wavelength of tungsten $\lambda =\frac{hc}{\varphi }$
$⟹$ $\frac{{\lambda }_W}{{\lambda }_{Na}}=\frac{{\varphi }_{Na}}{{\varphi }_W}$
Given : ${\lambda }_{Na}=5460$ ${\varphi }_W=4.4eV$ ${\varphi }_{Na}=2.3eV$
$\frac{{\lambda }_W}{5460}=\frac{2.3}{4.4}$
$⟹{\lambda }_W=2854$