If the work function of a metal is $3 \ eV$,then the threshold wavelength will be ............ $\mathring{A}$.

Two identical photo-cathodes receive light of frequencies $f_1$ and $f_2$. If the velocities of the photoelectrons (of mass $m$) coming out are respectively $v_1$ and $v_2$,then:

$A$ point source of light is used in a photoelectric effect experiment. If the source is moved farther from the emitting metal, then the stopping potential will

The work function of a substance is $3.0 \ eV$. The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately: (in $nm$)

The retarding potential for having zero photo-electron current:

Photoelectric emission is observed from a metallic surface for frequencies $v_1$ and $v_2$ of the incident light rays $(v_1 > v_2)$. If the maximum values of kinetic energy of the photoelectrons emitted in the two cases are in the ratio of $1:k$,then the threshold frequency of the metallic surface is