Potential Difference:

Potential Difference: Work done in bringing a unit positive charge from one point to other point is the potential difference between the two points. Its SI unit is volt and is a scalar quantity.

Electric Capacity: Electric capacity of a conductor is defined as the charge required increasing the potential of the conductor by unity. If potential of a conductor is increased by V when a charge Q is given to it, capacity of the conductor is Q / V. Its SI unit is farad. (F)

Electrochemical Cell: Electrochemical cell is a device which converts chemical energy into electrical energy.

Primary Cell: In primary cell electrical energy is obtained from the irreversible chemical reaction taking inside cell. After complete discharge, primary cell becomes unserviceable.

Examples: Voltaic Cell, Leclanche Cell, Dry Cell etc.

Secondary Cell: A secondary cell is that which has to be charged at first from an external electric source and then can be used to draw current. Such cells are rechargeable.

Production of electricity by chemical reation was first discovered by Allexandro de volta (voltaic cell is named after him) in 1794. In voltaic cell zinc rod is used as cathode and copper rod is used as anode. These rods are placed in sulphuric acid kept in a glass vessel.

In a Leclanche cell, carbon rod acts as anode and zinc rod acts as cathode. These rods are placed in ammonium chloride kept in a glass vessel.

The emf of Leclanche cell is 1.5 volt.

Leclancle cell is used for intermittent works. I.e. works in which continuous electrical energy is not required like electric bell.

In a dry cell, mixture of MnO₂, NH₄ CI and carbon is kept in a zinc vessel. A carbon rod is placed in the mixture which acts as anode. The zinc vessel itself acts as cathode the emf of dry cell is 1.5 volt.