Question

The work functions of tungsten and sodium are $5.06eV$ and $2.53eV$ respectively. If threshold wavelength of sodium is $5896\mathring{A}$ , then the threshold wavelength of tungsten will be

• A. $11792\mathring{A}$
• B. $5896\mathring{A}$
• C. $4312\mathring{A}$
• D. $2948\mathring{A}$

Answer 1

The correct option is D $2948\mathring{A}$

The work function of a metal is given as

$K_{max}=\frac{hc}{\lambda }-\varphi$

The threshold wavelength occurs when$K_{max}=0$

Then the threshold wavelength will be

${\lambda }_t=\frac{hc}{\varphi }$

$=\frac{\left(4.136\times {10}^{-15}eV.\sec \right)\left(3\times {10}^8\frac{m}{\sec }\right)}{5.06eV}$

${\lambda }_t=2948\stackrel{0}{A}$