The threshold wavelengths for photoelectric emission from two metals $A$ and $B$ are $400 \ nm$ and $800 \ nm$ respectively. The ratio of their work functions,$\phi_{A} : \phi_{B}$ is:

In the photoelectric effect, the kinetic energy of the electron emitted from the metal surface depends upon:

The maximum kinetic energy of the photoelectrons varies:

Let $v$ be the frequency of the incident photon and $v_0$ be the threshold frequency. The condition for the emission of photoelectrons is:

Two radiations of photon energies $1 \; eV$ and $2.5 \; eV$ successively illuminate a photosensitive metallic surface of work function $0.5 \; eV$. The ratio of the maximum speeds of the emitted electrons is

When photons of energy $8 \times 10^{-19} \ J$ are incident on a photosensitive material,the de Broglie wavelength of the photoelectrons emitted with maximum kinetic energy is $10 \ Å$. The work function of the photosensitive material is nearly (in $eV$)