Question

Photoelectric effect takes place in element A. Its work function is $2.5eV$ and threshold wavelength is $\lambda$. An other element $B$ is having work function of $5eV$. Then find out the wavelength that can produce photoelectric effect in $B$

• A. $\frac{\lambda }{2}$
• B. $2\lambda$
• C. $\lambda$
• D. $3\lambda$

Answer 1

Answer: (A)

$\frac{\lambda }{2}$

We know the relation between work function, $W$ and threshold wavelength, $\lambda$ is $W=\frac{hc}{\lambda }$

or $\lambda \propto \frac{1}{W}$

Using above relation we notice that work function for $B$ is $double$ of that for $A$ so the threshold wavelength for $B$ will be $half$ of that for $A$ that is answer is $\frac{\lambda }{2}$