ELECTRICITY

Electricity has an important

role in our day to day life.

It is a controllable

and convenient

form of energy.

You must have seen in cartoons and movies

, toons with

electric powers So....

We know that flowing of

water forms a water current.

Similarly if electric charge flows through a conductor, it

is called electric current.

A continuous and closed path

of an electric current is

called circuit

So electric current was considered to flow of positive charges and direction of flow of positive charges was taken to be direction of electric current .

Electrons constitute the flow of charge in circuit.

Conventionally in an electric circuit the direction of electric current is taken as opposite to the direction of flow of electrons which are negative charges.

Electrical current is expressed by the amount of

charge flowing through a particular area in unit times.

If a net charge Q, flows across any cross section area of a conductor in time t, then

the current I is :-I= Q/t

The SI unit of electric charge is coulomb (C), which is equivalent to charge contained in nearly 6x1018

electrons.And an electron possesses a negative charge of 1.6 x

10-19 C.

I is expressed by unit called Ampere(A)

Current is measured by an instrument called AMMETER

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HOW DOES ELECTRONS FLOW?

Let us take analogy of water flow. If one

end of horizontal pipe is connected to

a tank at higher level such that there

is a pressure difference between two ends of pipe, then water flows from other end.

Similarly electrons only move when there is a difference of electric pressure called POTENTIAL DIFFERENCE-along the conductor. This difference can be produced by battery. Within it the chemical action generates potential difference across the terminals.

Potential difference is expressed by the

WORK DONE to move a unit charge from one

point to anotherPotential difference (V) between two

points=Work done/ charge(Q) V= W/Q

The SI unit of potential difference is volt (V), which is named after a scientist Alessandro Volta.

V is expressed by unit called VOLT (V)

It is measured by an instrument called VOLTMETER

It is often convenient to draw a schematic diagram, in which different components of circuit

is represented by symbols

EXAMPLE

Symbolic circuit diagram

OHM’s LAWOhm’s law states that potential

difference (V), across the ends of a given metallic wire is directly proportional to

the current flowing it, provided its temperature remains constantV I

or V =IR

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What will be “Graph of ohm’s law”

R is a constant for the given metallic wire at a given temperature and is called resistance, it is the property of a conductor to resist the flow of charges through it.

Its SI unit is ohm represented by Greek symbol Ω. According to ohm’s law:-R=V/I Also I=V/R

A straight line plot shows that as the current

through a wire increases then the potential

difference across the wire increases

SIMPLE FORMULA TRIANGLE TO LEARN RELATION OF V,I&R

FACTORS AFFECTING RESISTANCE OF A CONDUCTOR

With increase in length, charges will have to travel a longer

distance in resisting conductor. Resistance will increaseWith increase in cross

section area, there will be more space for charges so as

result less resistance

Resistance also depends on temperature

In length

In cross section areaIn temperature

Therefore R α L R α L/a R =ρL/aWhere l is length , a is area of cross

section and ρ (rho) is constant of proportionality

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ρ(rho), is called electrical resistivity of the material of

conductor. The SI unit of resistivity is Ωm. It is a

characteristic property of material. Both resistance and resistivity vary with

temperature.

PRESENTED BY:- UTKARSH KUMARCLASS :- 10TH