Question

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

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

Answer 1

Answer: (B)

Since, ${\varphi }_0=\frac{hc}{{\lambda }_0}$;
so $\frac{{\varphi }_{0_r}}{{\varphi }_{0_{\text{Nu }}}}=\frac{{\lambda }_{Na}}{{\lambda }_T}$
or ${\lambda }_T={\lambda }_{Na}\times \frac{{\varphi }_{0_N}}{{\varphi }_{0_T}}$
$=\frac{5460\times 2.3}{4.5}=2791\mathring{A}$