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

Light with a frequency of $1.5$ times the threshold frequency is incident on a photosensitive material. If the frequency is halved and the intensity is doubled,what will be the photoelectric current?

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

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:

$A$ monochromatic beam of light of wavelength $400\,nm$ is incident normally upon a photosensitive surface ($25\%$ reflects and the rest is absorbed). This produces a radiation pressure of $5 \times 10^{-7}\,N/m^2$ on the surface. If $0.1\%$ of the incident photons produce photoelectrons,the corresponding saturation current will be $\dots \mu A$. (Consider the area of the photosensitive surface $= 5\,cm^2$)

$A$ small metal ball is suspended in a uniform electric field with the help of an insulated thread. If a high energy $X-$ray beam falls on the ball,then the ball