Current Carriers

(a) Current carriers in solid conductors :

In solid conductors like metals, the valence electrons of the atoms do not remain attached to individual atoms but are free to move throughout the volume of the conductor.

Under the effect of an external electric field, the valence electrons move in a definite direction causing electric current in the conductors.

Thus, valence electrons are the current carriers in solid conductors.

(b) Current carriers in liquids :

In an electrolyte like NaCl etc., there are positively and negatively charged ions (like Na+ , Cl-).

These are forced to move in definite directions under the effect of an external electric field, causing electric current.

Thus, in liquids, the current carriers are positively and negatively charged ions.

(c) Current carriers in gases :

Ordinarily, the gases are insulators of electricity.

They can be ionized by applying a high potential difference at low pressure

Thus, positive ions and electrons are the current carriers in gases.

Units of electric current:-

(a) C.G.S. electro-static unit (esu):- 1 esu of current (stat-ampere) = 1 esu of charge/1 second

(b) C.G.S. electro-static unit (emu):- 1 emu of current (ab-ampere) = 1 emu of charge/1 second

(c) S. I unit (ampere):- 1 ampere = 1 coulomb/1 second

(d) 1 A = 3×10⁹esu of current or stat-ampere

(e) 1 A = 1/10 emu of current or abampere