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

According to Einstein's photoelectric equation, the graph between the kinetic energy of photoelectrons ejected and the frequency of incident radiation is

A 1$\mu$ $A$ beam of protons with a cross-sectional area of $0.5$ sq. mm is moving with a velocity of $3 \times {10^4}m{s^{ - 1}}$. Then charge density of beam is

A beam of electromagnetic radiation of intensity $6.4 \times 10^{-5}\; \mathrm{W} / \mathrm{cm}^{2}$ is comprised of wavelength, $\lambda=310 \;\mathrm{nm} .$ It falls normally on a metal (work function $\varphi=2 \;\mathrm{eV}$ ) of surface area of $1\; \mathrm{cm}^{2} .$ If one in $10^{3}$ photons ejects an electron, total number of electrons ejected in $1 \;s$ is $10^{\mathrm{x}}$.then $\mathrm{x}$ is

$\left(\mathrm{hc}=1240\; \mathrm{eV} \mathrm{nm}, 1\; \mathrm{eV}=1.6 \times 10^{-19} \;\mathrm{J}\right)$

When radiation of wavelength $\lambda $ is incident on a metallic surface, the stopping potential is $4.8\, volts$. If the same surface is illuminated with radiation of double the wavelength, then the stopping potential becomes $1.6\, volts$. Then the threshold wavelength for the surface is

A convex lens of focal length $40 \mathrm{~cm}$ 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 $20 \mathrm{~cm}$. The photoelectric current now is: