The work functions of Caesium $(Cs)$, Potassium $(K)$, and Sodium $(Na)$ are $2.14\,eV$, $2.30\,eV$, and $2.75\,eV$ respectively. If incident electromagnetic radiation has an incident energy of $2.20\,eV$, which of these photosensitive surfaces may emit photoelectrons?

The photo-electrons emitted from a surface of sodium metal are such that

The work function of a metal is

Photoelectric effect is produced by a point source on a small metal plate. Which of the following curves represents the saturation photoelectric current as a function of the distance between the source and the metal?

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:

In a dark room of photography,generally red light is used. The reason is