Question

If the wavelength is brought down from $6000\mathring{A}$ to $4000\mathring{A}$ in a photoelectric experiment, then what will happen ?

• A. The work function of the metal will increase
• B. The threshold frequency will decrease
• C. No change will take place
• D. Cut off voltage will increase

Answer 1

The correct option is D Cut off voltage will increase

We know,

Stopping potential (or cut off voltage) is given by $V_o=\frac{hc}{e}\left(\frac{1}{\lambda }\right)-\frac{\varphi }{e}$

where $\lambda$ is the wavelength of the incident photon.

Since work function $\varphi$ is the property of the metal surface, thus it does not depend on the wavelength of incident photon. Hence $\varphi$ remains the same.

As per the equation,

when the wavelength of the incident photon decreases, the stopping potential will increase according to the equation.