Electricity Is One of the Most Important Source of Energy. It Has Become an Indispensable

Electricity

Electricity is one of the most important source of energy. It has become an indispensable part of our life. It is used in home and in industry for various purposes, such as lighting, heating, operating machines and so on.

Potential due to a Charge

The process of depositing an electric charge, for example a positive charge on a body is known as charging the body. Initially the body has no charge on it; it now acquires a small amount of charge. If one wishes to deposit some more charge of the same kind on that body, this charge will experience a force of repulsion, due to charges already present on the body. Therefore, some work has to be done to counter this force of repulsion. The work done on electrical charge in the process of charging gets stored as potential energy of charges. This potential energy is called electrostatic potential or just potential.

The electrostatic potential at any point is defined as the work done in bringing a single positive charge from infinity to that point. The unit of potential is Volt (V)

A potential of one volt at a point implies that the amount of work done to bring one coulomb of positive charge from infinity to that point is one joule.

Thus if a body is given Q coulomb of charge to raise its potential by V volt, then the amount of work done will be VQ joule

1 Electric Current

If two objects charge to different potential are placed side by side , charges will not move from one to the other. Now if the two are connected, using a wire or a conductor, the flow of charges take place. Charge will flow as long as there is a difference of potential between the two. The flow stops as soon as their potentials become equal. This flow of electric charge is called electric current.

The potential difference (p.d.) of one volt between two points is the measure of work done in moving one coulomb of charge across them. p.d= Work done / charge moved= W/Q= Joule/Coulomb= volt (equation-2)

One simple way of maintaining a potential difference between the two ends of a conductor is to connect it to battery or a dry cell. With the help of battery or a cell, the potential difference between two electrodes is maintained by chemical processes going on inside it, between the electrodes and the electrolytes.

What is an Electric circuit ?

Electric Circuit is an arrangement for obtaining electric current in a conductor by connecting it to a source of electric current.

The magnitude of the current I is the charge flowing in the circuit in one second.

I =Q/T= Charge/ time

Q is the charge in coulomb flowing in t second. If one coulomb of charge flows through the circuit in one second, the current in the circuit will be 1 ampere, which is the unit of the current.

When a charge flows across a p.d , the work done= electrical energy involved =V.Q.=V. I.t

2 An ammeter is an instrument used for measuring current in a circuit. Ammeter should be connected in such a way that whole current flows through it. This way of connecting ammeter is called series connection.

Voltmeter is an instrument used for measuring potential difference between two points.

The picture of an ammeter and voltmeter is as under:

As compared to ammeter, voltmeter is joined as an addition to an already completed circuit. The voltmeter is connected across a connection. This way of connecting voltmeter is called parallel connection.

Ohm’s Law – Resistance

In an experiment that studies the variation of current with changing potential difference, it has been found that there is direct proportion between potential

3 difference and the electric current. The graph between the current and the potential difference is a straight line.

This relationship can be represented as V= (constant) x I

The current in the circuits is not decided by the battery. But the components of the circuit determine how much current they will draw from the given battery. Some materials allow larger current to flow through them than others. In other words, certain materials offer more resistance to the flow of current than others.

Electrical Resistance or Resistance is the property of a material due to which it opposes or limits the flow of electric current through it.

The resistance of the conductor can be defined in terms of current passing through it and the potential difference across its ends. The resistance is defined as the ratio of potential difference V across its ends and the current I flowing through it.

R= V/I

4 Potential differences’ unit is volt and the unit of current is ampere, the unit of resistance is volt/ampere. The unit of resistance is called the ohm, named after George Simon Ohm, who discovered the relations V= constant X I and R= V/I

Ohm’s law states that the current in a circuit is proportional to the voltage across it. It also states that the resistance in a circuit is the ratio of the voltage to its current. One ohm is the resistance of a conductor through which a current of 1 ampere flows when the potential difference across its ends is one volt.

An important role is played by the resistance in electrical circuits. The parts or components of a circuit which are to provide a path for the movement of charges are made from materials with low resistance. These are called Conductors. Conductors allow electricity to pass through them.

Often some parts or components of the circuit are intentionally designed for offering high resistance. These are made of materials with a high resistance which are called resistors. A substance that has infinitely high resistance will not allow electricity to flow through. It is called an insulator. Rubber is an excellent insulator.

Electric Power

Power is the rate at which work is done. In an electric circuit, the work done in a time t is given by When a charge flows across a p.d , the work done= electrical energy involved =V.Q.=V. I.t Therefore, Power P= W/t = VI

If p.d. is measured in volt and current in ampere, the unit of Power is volt ampere, also called a watt.

1 volt x ampere= 1 Joule/ 1 coulomb x 1 coulomb/ 1 second= 1 Joule/1 second= 1 watt.

Thus unit of electric power is watt. Electric power is the rate at which the energy is consumed by the ciruit. If an appliance of 1000 watt or one kilowatt is connected to the circuit, it will consume 1 KJ of electric energy in one second.