If the threshold wavelength for sodium is $5420 \mathring{A}$,then the work function of sodium is ............ $eV$.

If the threshold wavelength of light for photoelectric emission to take place from a metal surface is $6250 \ \text{Å}$, then the work function of the metal is (Planck's constant $= 6.6 \times 10^{-34} \ \text{Js}$) (in $\text{eV}$)

$A$ photon of wavelength $3315 \ \text{Å}$ falls on a photocathode and an electron of energy $3 \times 10^{-19} \ \text{J}$ is ejected. The threshold wavelength of the photon is [Planck's constant $(h)$ $= 6.63 \times 10^{-34} \ \text{J-s}$, velocity of light $(c)$ $= 3 \times 10^{8} \ \text{m/s}$]. (in $\text{Å}$)

The threshold wavelength for photoelectric emission in tungsten is $400 \ nm$. The wavelength of light that must be used in order to eject electrons with a maximum kinetic energy of $0.9 \ eV$ is .............. $nm$.

Electrons are emitted with kinetic energy $T$ from a metal plate by an irradiation of light of intensity $J$ and frequency $v$. Then, which of the following will be true?

$A$ photon of energy $hv$ is absorbed by a free electron of a metal having work function $\phi < hv$.