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# Electricity

## Introduction

Electricity is one of the most important sources of energy. Lights, fans, motors, radios and television are some common appliances which work on electricity.

## Electric Potential and Potential Difference

'Electrical potential' is a condition, which determines the direction of the flow of charge.

## Electricity and Flow of Charge

If two charged bodies of different potentials are placed one beside the other, the charges will not move from one body to the other.

## Components of Electrical Circuits

The devices which deliver electricity are called the 'sources'and lamps, electric engines, etc. which consume electricity are called 'loads'. Switches are used to switch the loads on and off whenever necessary.

## Ohm's Law

George Ohm showed that the flow of electric current through a wire depended on its 'resistance' and the potential difference between its ends.

## Combination of Resistors in Series and Parallel

Resistors can be combined in different ways. When two or more resistors are connected end to end consecutively, so that the same current flows through all of them then, the resistors are said to be in series.

## Factors Affecting Resistance

Resistance of a conductor is directly proportional to the length of the wire i.e., longer the wire greater will be the resistance and shorter the wire smaller will be the resistance.

## Resistors in Series

The equivalent resistance is the sum of the individual resistances connected in series. The above result can be generalised for 'n' number of resistances of different values as R = R1+ R2 +............ + Rn.

## Law of Combination of Resistors in Parallel

If the resistors are connected in parallel, the reciprocal of the equivalent resistance is equal to the sum of the reciprocals of all the individual resistances.

## Electric Power and Its Derivation

Power is the rate of doing work or in other words, it is the work done in one second.

## Summary

Electric potential is the condition that determines direction of flow of charge. Electrical potential at a point in an electric field is defined as the amount of work done in bringing a unit positive charge from infinity to that point.

## Multiple Choice Questions

*AP and SAT are registered trademarks of the College Board.