If the intensity of incident light on a metal surface is decreased,then . . . . . .

The work functions of Caesium $(Cs)$, Potassium $(K)$, and Sodium $(Na)$ are $2.14\,eV$, $2.30\,eV$, and $2.75\,eV$ respectively. If incident electromagnetic radiation has an incident energy of $2.20\,eV$, which of these photosensitive surfaces may emit photoelectrons?

$A$ convex lens of focal length $40 \ cm$ forms an image of an extended source of light on a photoelectric cell. $A$ current $I$ is produced. The lens is replaced by another convex lens having the same diameter but focal length $20 \ cm$. The photoelectric current now is:

The graph given in the figure shows the variation of photocurrent $(I)$ with the applied voltage $(V)$ for two different materials and for two different intensities of incident radiation. Which of the following pairs of curves represent the same material?

Describe Hallwach's and Lenard's observations regarding the photoelectric effect in short.

The figure shows a plot of photo current versus anode potential for a photo sensitive surface for three different radiations. Which one of the following is a correct statement?