Question

Assertion :Threshold wavelength of certain metal is ${\lambda }_0$. Light of wavelength slightly less than ${\lambda }_0$ is incident on the plate. It is found that after some time the emission of electrons stops Reason: The ejected electrons experience force of attraction due to development of positive.

• A. Assertion is incorrect but Reason is correct.
• B. Both Assertion and Reason are correct and Reason is not the correct explanation for Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Both Assertion and Reason are incorrect and Reason is correct explanation for Assertion.

Answer 1

The correct option is A Assertion is incorrect but Reason is correct.

As we decrease $\lambda$ to less than it's threshold wavelength so due to the fall of sufficient energy the electrons will come out continuously it will not stop after some time and obviously the ejected electron will experience attraction from surface electrons which becomes positively charged after the electron.