I was studying Halliday Resnick Walker, where it says that during electrical breakdown, when electric field crosses Ec of air, the electrons move through air, colliding with its atoms and the atoms, therefore, emitting light as sparks. Then why don't we see sparks in wires carrying current, since electrons are moving through it and colliding with atoms of wire?
A spark is a bit of incandescent gas. 'in wires' we don't have enough heat to make the metal incandescent, and if we did, the wire is opaque,so we wouldn't see it.
Wire is useful for conducting electricity precisely because it does NOT evaporate when electricity passes through.
sparks are created due to exitation and de-exitation of electrons in a particular orbit,in the case of a conductor the electrons are delocalized,(they are in a sea of electrons,so rather a lot more energy is required in order for the de-exited electron to emit energy in the visible range...eg:-a high current through a small pencil lead will cause a bright red glow. cheers.