Explain emission of electron from metal.Define work function .Write its unit,work function of metal depend on which factors?

Explanation

Normally electron cannot escape from the surface of metal.
When temperature of metals is increased,kinetic energy due to oscillation increases.When this energy due to oscillation increases.When this energy exceed binding energy,electron will positively charged.
But due to attractive force between positive ion and negative ion,surface and it will become positively charged.
But due to attractive force between positive ion and negative ion,electron again attracted to metal surface.
If energy of electron is more than energy due to attractive force,then only it can escape from metal surface.
Work function:minimum energy required to make an electron escape from the metal surface is called work function of the metal.
Work function is denoted by `phi_(o)` Its SI unit is eV (electron volt).
Work function of metal depends on type of metal and surface.