Electricity and Magnetism - 1 — PHYSICS STD 9 — Question

(i) Flow of electric current in solids : In solids, the positive charges are associated with atomic nuclei. As the nuclei are firmly packed and closely held by inter-atomic forces, therefore, positive charges cannot drift.
On the other hand, negative charges (electrons) are not held firmly. Thus, when a potential difference, however small, is applied they start drifting from lower to higher potential.
The continuous drift of electrons, through the body of a solid conductor constitutes the current.
(ii) Flow of electric current in liquids: Within a liquid no electrons move. However, when a negatively charged and a positively charged electrodes are placed in a liquid, it sets up an electric field.
Under the influence of the electric field, the positively charged ions migrate towards the negatively charged electrode and vice versa.
At the cathode the positively charged ions gain electrons. At the anode the negatively charged ions lose same number of electrons.
Thus, in a way number of electrons given by the cathode is equal to the number of electrons accepted by the anode. The sum up, we can say that simultaneous movement and discharge of positive and negative ions in the opposite directions constitutes the current in the liquids.