The work function of aluminium is  $4.2eV.$ If two photons, each of energy $3.5 eV$strike an electron of aluminium, then emission of electrons will be

How many photons are emitted by a laser source of $5 \times 10^{-3} \,W$ operating at $632.2 \,nm$ in $2 \,s$ is .......$\times 10^{16}$ $\left(h=6.63 \times 10^{-34} \,Js \right)$

In a photoelectric effect experiment a light of frequency $1.5$ times the threshold frequency is made to fall on the surface of photosensitive material. Now if the frequency is halved and intensity is doubled, the number of photo electrons emitted will be:

Photoelectric effect was successfully explained first by

In photoelectric effect, the electrons are ejected from metals if the incident light has a certain minimum

The energy equivalent to $1\,mg$ of matter in $MeV$ is