A voltage source has the ability to convert energy of some form (e.g. mechanical, chemical, heat etc.) into electrical energy and transfer it into the circuit into which it is connected.

There are different types of sources of emf such as chemical cell, voltaic cell (or) a Dry battery.

Voltaic Cell: In a simple voltaic cell, copper and zinc electrodes are used. These electrodes are immersed in a dilute H₂SO₄ solution, which is kept in a glass vessel. The copper electrode is the positive electrode and the zinc electrode is the negative electrode. The conventional direction of current is taken as that from copper to zinc. The emf of the cell is maintained by the reaction of the zinc electrode which is dipped in dilute H₂SO₄.

Dry Battery: A dry battery is a portable form of Leclanche cell. It consists of zinc vessel filled with a paste of ammonium chloride, zinc chloride and sawdust. Zinc vessel acts as negative electrode. Carbon rod surrounded by charcoal MnO₂ and plaster of paris is used as a positive electrode.
A glass bottle containing a concentrated solution of ammonium chloride is used in this cell. An amalgamated zinc electrode is dipped in this solution. Carbon electrode is used as positive electrode, which is placed in a porous pot P. This porous pot P is filled with manganese dioxide and charcoal powder, and acts as a depolariser that is the depolarizer prevents concentration of any one ion on the electrodes.

Car Battery: A car battery is a lead accumulator cell. An accumulator is a voltage source that can repeatedly accumulate more charges on its electrodes. A lead accumulator is known as a secondary cell because it can be recharged when its initial charge is exhausted.