Current Electricity

Current Electricity 

Notes for Class 11 - 12

Ohm's law

Electricity flows when there is a potential difference between the ends of a conductor. In 1877 German scientist George Simon Ohm carried out an experiment on how electricity.


The property of a conductor which opposes the flow of current is called the resistance of that conductor.


The amount of electrical energy spent in one hour by a device having a power of 1 kilowatt is called a kilowatt-hour (kWh).

Electrical cell

The device by means of which electric energy is produced from chemical energy and the flow of current is kept ongoing is called an electrical cell.

Electromotive force

The work done to bring one unit of charge along with the electric cell from one point to that point by rotating it through the whole circuit, i.e. the amount of energy supplied by the electric cell to keep the flow in motion is called electromotive force of that cell.

Wheatstone bridge

If a closed rectangular circuit is made by establishing four corners and at two opposite ends of the circuit a galvanometer, and at other two ends an electric source is connected then that circuit is said to be a Wheatstone bridge circuit.


A very small resistance that is used in devices by connecting to it in parallel combination so that excess current can pass through it in order to protect the electrical device from damage due to excess current flow is called a shunt.


The device by means of which electromotive force of a cell and the potential difference between any two points of an electrical circuit can be determined through a potential drop system is called a potentiometer.

Meter Bridge

The device to which a one-meter long wire having uniform cross-sectional resistance is connected in order to determine the resistance of the components of the wire, i.e specific resistance of the wire by Wheatstone's bridge principle is called a meter bridge.

Post Office Box

The resistance box whose resistances can be considered as the three arms of a Wheatstone bridge and by bears of whose fourth arm the general value of an unknown resistance can be determined through Wheatstone's bridge principle is called Post Office Box.

Two Laws of Kirchhoff

First law: In an electric circuit, the algebraic sum of current into a junction is zero. 

Second law: In any closed circuit, the algebraic sum of the products of current and resistance of each part of the circuit is equal to the total electromotive force in the circuit.

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