The photoelectric threshold wavelength of a certain metal is $3000 \mathring{A}$. If the radiation of $2000 \mathring{A}$ is incident on the metal,then:

$A$ photocell is illuminated by a small bright light source placed at a distance of $1 \ m$. When the same light source is placed at a distance of $\frac{1}{2} \ m$,the number of electrons emitted by the photocathode will be:

How many times more photons are emitted from a photocell by a source placed at a distance of $1 \ m$ compared to a source placed at a distance of $2 \ m$?

$A$ 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 variation of photoelectric current with anode potential is shown below. Choose the correct option ($V_0$ = stopping potential).

The value of the stopping potential in the following diagram is ......... $V$.