An isolated metallic sphere is illuminated by light of $4\,eV$ photon energy. If the work function of the metal is $2\,eV$,then the minimum potential of the sphere so that no photoelectrons are ejected is ................ $V$.

The threshold wavelength for the photoelectric effect of a metal is $6500 \mathring{A}$. The work function of the metal is approximately .......... $eV$.

The work function of nickel is $5 \text{ eV}$. When light of wavelength $2000 \text{ Å}$ falls on it,it emits photoelectrons. The potential difference necessary to stop the fastest emitted electrons is (given $h = 6.67 \times 10^{-34} \text{ J-s}$): (in $\text{ V}$)

Explain: "For photoelectric emission, the frequency of incident radiation should be greater than the threshold frequency."

The work functions of metals $A$ and $B$ are in the ratio $1 : 2$. If light of frequencies $f$ and $2f$ are incident on the surfaces of $A$ and $B$ respectively,the ratio of the maximum kinetic energy of photoelectrons emitted will be ($f$ and $2f$ are both frequencies greater than the threshold frequency of metals $A$ and $B$).

When a certain metallic surface is illuminated with monochromatic light of wavelength $\lambda$,the stopping potential for photoelectric current is $4 V_0$. When the same surface is illuminated with light of wavelength $3 \lambda$,the stopping potential is $V_0$. The threshold wavelength for this surface for the photoelectric effect is