Question

The work function for tungsten and sodium are $4.5eV$ and $2.3eV$ respectively. If threshold wavelength $\lambda$ for sodium is $5460\mathring{A}$, the value of $\lambda$ for tungsten is

• A. $5893\mathring{A}$
• B. $10683\mathring{A}$
• C. $2791\mathring{A}$
• D. $528\mathring{A}$

Answer 1

The correct option is C $2791\mathring{A}$

Work function, $W=\frac{hc}{\lambda }$,

where $h$ and $c$ are Planck's constant and speed of light respectively so both are constant.

so $W\propto \frac{1}{\lambda }$, where $\lambda$ is threshold wavelength.

Or $\frac{W_N}{W_t}=\frac{{\lambda }_t}{{\lambda }_N}$

so ${\lambda }_t=\frac{{\lambda }_N{W}_N}{W_t}=\frac{5460\times 2.3}{4.5}=2790.66Angstrom$ nearly $2791Angstrom$