Light of wavelength $4000 \ \mathring A$ is incident on a sodium surface,where the threshold wavelength for photoemission is $5420 \ \mathring A$. The work function of sodium is ............ $eV$.

In the photoelectric effect,if a radiation of weak intensity is used instead of a radiation of strong intensity,but of the same suitable frequency,then:

The curves $(1)$,$(2)$,$(3)$,and $(4)$ show the variation between the applied potential difference $(V)$ and the photoelectric current $(i)$ at two different intensities of light $(I_1 > I_2)$. In which figure is the correct variation shown?

Light of wavelength $4000 Å$ is incident on a sodium surface for which the threshold wavelength of photoelectrons is $5420 Å$. The work function of sodium is (in $eV$)

In the photoelectric effect,the photocurrent:

One milliwatt of light of wavelength $4560 \ \mathring{A}$ is incident on a cesium surface of work function $1.9 \ eV$. Given that the quantum efficiency of photoelectric emission is $0.5\%$. Planck's constant $h = 6.62 \times 10^{-34} \ J \cdot s$,velocity of light $c = 3 \times 10^8 \ m/s$,the corresponding photoelectric current is: