After a photon is incident on a metal surface,the time taken for the emission of a photoelectron from the surface is approximately ...........

Which of the following statements is correct regarding the photoelectric effect?

Threshold frequency for a metal is $10^{15} \ Hz$. Light of $\lambda = 4000 \ \mathring{A}$ falls on its surface. Which of the following statements is correct?

"With increase in frequency of light incident, number of electrons emitted increase" - True or false?

In the photoelectric effect,electrons are ejected from metals if the incident light has a certain minimum:

The material of the cathode in a photocell is changed such that the work function of the surface changes from $W_1$ to $W_2$ $(W_2 > W_1)$. If the photocurrents emitted before and after changing the cathode surface are $I_1$ and $I_2$ respectively,and $hf > W_2$,then: