why is the transfer of charge always a surface phenomenon? (electrostatics)?

Question

my college professor asked this question, and i wasn't able to find it anywhere....
please specify any books or websites that you may know.
thanx.

Answer 1

It is a indeed surface phenomenon.

Since air is the ubiqutous dielectric medium having low electrical conductivity ,whatever charge transfer occurs through it(although minuscle) is mainly due to surface electrons.

The above phenomenon is due to the excess energy possessed by the surface electrons which are on the verge of escaping from an electrically charged body.

However when the dielectric width of air reduces and direct contact occurs charge transfer takes place from the entire body but it still occurs through the surface so its a surface phenomenon!

Answer 2

Because air is a pretty good insulator.

Charges build up in things because air (or whatever's keeping the object from ground) is enough of an insulator to prevent discharge. An object's surface is what separates it from the air, or from other objects. When that low-conductivity air gap is removed and two surfaces come into contact, bam!