Question

In the photoelectric effect why do photon takes out any one electron when it strikes the metal?If electron can be emitted by striking the light(photon) then why cant light be emitted by striking the electron over the metal?

Answer 1

The photoelectric effect only describes how a metal reacts when hit with light. It was used as Einstein's starting point to show that light is made of particles. If you hit metal with an electron with enough energy you can also knock electrons off the metal because electrons are also particles, but that was not surprising to anyone in 1905 because they already knew electrons were particles. Also when you hit metal with an electron and knock an electron off of an atom, a photon is released if the electron was in an inner valence. This is due to outer electrons "falling" to a lower orbit to take the place of the displaced electron. This is how an X-ray machine works. Electrons are allowed to accelerate in a high electric field and strike a metal target, and X-rays are thus emitted from the target. But that is different than the photoelectric effect because its not photons causing the electron to be ejected.