Common Sources of Electric Current


•    Cells and batteries of different shapes and sizes are common sources of electric current.


•    They convert chemical energy into electrical energy.


Cells are of Two Types:

Primary cell:

•    A primary cell is a battery that is designed to be used once only. It can’t be recharged with electricity and reused like a secondary cell.


Dry cell and mercury cell


Secondary Cell:

•    A secondary cell or battery is one that can be electrically recharged after use to their original pre-discharged condition, by passing current through the circuit in the opposite direction to the current during discharge.

Example : Batteries used in mobile phones, Lap tops, car batteries, Inverter batteries etc.

•    These days solar cells are commonly used in many applications. Many calculators are powered with solar cells.

•    Solar panels use light energy (photons) from the sun to generate electricity


Dry Cell:

•    Dry cell contains dry or semi solid ingredients. It is very convenient source of electric current.


Construction and working of a dry cell:

•    Dry cell contains a paste of ammonium chloride inside a Zinc container.

•    Inside the paste, a cardboard container containing powdered manganese dioxide and carbon is placed.

•    The cardboard container has microscopic holes in it, through which chemical components formed during chemical reaction pass.

•    A carbon rod capped with a metal is dipped into manganese di oxide.

•    The entire thing is then sealed (with only metal cap sticking out) so that contents do not spill out.

•    The Zinc can is also wrapped so that only the base is exposed.

•    The metal cap is the positive terminal of the electric cell. The metal disc is the negative terminal. All electric cells have two terminals; a positive terminal and a negative terminal. It can be considered that Electric current flows in from one terminal and flows out from the other.

•    If the tip of the metal cap and the base of the zinc can are connected by a metal wire, current will flow through it which may be used to light a bulb.

•    An electric cell produces electricity from the chemicals stored inside it. When the chemicals in the electric cell are used up, the electric cell stops