Question

If the wavelength of light in an experiment on photoelectric effect is doubled,

• A. The photoelectric emission will not take place.
• B. The photoelectric emission may or may not take place.
• C. The stopping potential will increase.
• D. The stopping potential will decrease.

Answer 1

Answer: (B), (D)

The stopping potential will decrease.
The photoelectric emission may or may not take place.

The photoelectric effect related with the incident light frequency $\left(\nu \right)$ by the following equation:
$E_k=e{V}_s=h\nu -\varphi$,

where, $\varphi$ is the work function of the material and $E_k$ is the kinetic energy of the photo electron.
Here, the wavelength of light in an experiment on photoelectric effect is doubled, that means the frequency of the light is become half. If the energy of the incident light is still grater than or equal to the work function of the material then the electron will emit otherwise not. And in this case stopping potential will decrease.

And as a result, the photoelectric emission will take place

So, the answers are options (B) & (D).