When the electromagnetic radiations of frequencies $4 \times 10^{15} \,Hz$ and $6 \times 10^{15} \,Hz$ fall on the same metal in different experiments,the ratio of maximum kinetic energy of electrons liberated is $1: 3$. The threshold frequency for the metal is ............... $\times 10^{15} Hz$.

In the experiment of the photoelectric effect,the stopping potential for a given metal is $V_{0}$ volts when radiation of wavelength $\lambda_{0}$ is used. If radiation of wavelength $2\lambda_{0}$ is used for the same metal,then the stopping potential (in volts) will be: [$e=$ charge on electron,$c=$ speed of light,$h=$ Planck's constant.]

When a photon of energy $6 \ eV$ is incident on a metal surface with a work function of $4 \ eV$,the minimum kinetic energy of the emitted photoelectrons is ......... $eV$.

$A$ monochromatic point source of light is placed at a distance $d$ from a metal surface. Photoelectrons are ejected at a rate $n$ per second,and with maximum kinetic energy $E$. If the source is brought nearer to a distance $d / 2$,the rate and the maximum kinetic energy per photoelectron become nearly

If two metals $A$ and $B$ are exposed to radiation of wavelength $350 \, nm$. The work functions of metals $A$ and $B$ are $4.8 \, eV$ and $2.2 \, eV$ respectively. Choose the correct option.

The threshold wavelength for photoelectric emission from a metal surface is $5200 \ \mathring A$. Which of the following sources will cause photoelectric emission from this surface?