CBSE Class 10 Science Notes Chapter 12 Electricity

Here I am going to provide you CBSE Class 10 Science Notes Chapter 12 Electricity. By going through Electricity Class 10 Notes you can revise the Electricity chapter in a very effective way. I hope that this will certainly help you in your studies!

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CBSE Class 10 Science Notes Chapter 12 Electricity

Introduction

Electricity is one of the forms of energy and it can be produced from other types of energy.
The word electricity has been derived from the Greek word 'elektron' being amber.

Electric charge and it's properties

There are two types of charge, i.e. positive (+ve) charge and negative (+ve) charge.
Charge carried by proton is positive.
Charge carried by electron is negative.
Loss of electron - Positive Charge
Gain of electron - Negative Charge

Properties of Electric Charge

Unlike charges attract each other and Like charges repel each other.
The force between two charges varies directly as the product of two charges varies directly as the product of two charges (q₁and q₂ ) and inversely as the square of the distance (r) between them. This is also known as Coulomb's Law , i.e.

Where k is a constant.

Electric charge is conserved.
Electric charge is additive.
Electric charge is quantised.

Conductors: Substances through which charges can easily pass are known as conductors. For example: Metals, aqueous solutions of salts,etc.

Insulators: Substances through which charges can not pass are called insulators. Insulators are also called dielectrics. For example: glass, pure water, gases, etc.

Electric Current

Electric Current is defined as the rate of flow of electric charge.

Electric Current is the quantity of charge flowing per unit time.
It is denoted by 'I'.
It's SI unit is ampere (A).
So, if a charge 'Q' flows through a conductor in a time 't', then current 'I' will be :

1 ampere = 1 coulomb/ 1 second
The direction of electric current is opposite to the flow of electrons.
1 coulomb : It is an quantity of charge which flows through a circuit when one ampere of current flows through it in one second.
1 mA = 10^-3 A and 1 µA = 10^-6 A

Electric Potential Difference

The work done in carrying unit positive charge from one point to the another point is called electrical potential difference.

It is denoted by 'V'.
It's SI unit is volt (V).
[ 1V = 1J/C ]
Electric Current flows from higher potential to lower potential.

Ohm's Law

It was given by George Simon Ohm.
According to the Ohm's law, if physical conditions like temperature,etc of a conductor are kept unchanged, the strength of the current flowing through it is directly proportional to the potential difference across its ends.

V ∝ I
V = RI
I = VR
R = VI

Where, R is constant for the given conductor at a given temperature and is called resistance.

Resistance

The resistance of a conductor is the ratio of potential difference across its end to the strength of the current flowing through it.

The value of resistance depends on (i) size of conductor (ii) nature of the material (iii) the temperature of conductor.
It is obstruction to the flow of electrons in a conductor.
It's SI unit is ohm (Ω).
1Ω = 1V/1A
A resistor is an object of some conducting material having resistance of a desired value.

Drift Speed : The average speed with which the electrons drift in a conductor having a potential difference across its ends called the drift speed.

Factors on which resistance of a conductor depends

a) Nature of Material : Some materials create least hindrance and hence, are called good conductors. Silver is the best conductor of electricity. While some other materials create more hindrance in the flow of electric current, i.e. flow of electrons through them. Such materials are called bad conductors. Bad conductor are also known as insulators. Hard plastic is the one of the best insulators of electricity.

b) Length : If the length of the conductor increases the electrons have to travel and largest distance and as a result its resistance increases. Thus,

( R ∝ l ) ......(i)

c) Cross-sectional area : If the cross sectional area of the conductor decreases, the electrons find it more difficult to pass through it and as such its resistance increases. Thus,

( R ∝ 1/A ).....(ii)

Combining equation (i) & (ii) we get,

R ∝ lA
R = ρ lA

Where, ρ (rho) is the proportionality constant. It is called the electrical resistivity of the material of conductor.

Resistivity

Resistance of a conductor in its unit cross section area and unit length is called resistivity.

ρ = RAl

S.I. unit of resistivity (ρ) is Ωm.

Range of Resistivity in:

Conductors : 10-8 Ωm to 10-6 Ωm
Semiconductors : 10-5 Ωm to 103 Ωm
Insulators : 10¹² Ωm to 10¹⁷ Ωm

Combination of Resistors

In Series Combination

When resistors are joined from end to end, it is called in series. In this case, the total resistance of the system is equal to the sum of the resistance of all the resistors in the system.

Let, three resistors R1, R2, and R3 get connected in series.
Potential difference across A and B = V
Potential difference across R1, R2 and R3 = V1, V2 and V3
Current flowing through the combination = I
We, know that
V= V1 + V2 + V3 …. (i)
According to Ohm’s Law :
V1 = IR1, V2 = IR2 and V3 = IR3 ….. (ii)
Let, total resistance = Rs
Then, V = IRs …(iii)
From equations (i) and (ii) and (iii)
IRs = IR1 + IR2 + IR3
Rs = R1 + R2 + R3
When the resistors are connected in series, the current flowing through each resistor is the same and is equal to the total current

If n resistors are connected, each of value R then ,

[ Rs = nR ]

In Parallel Combination

When resistors are joined in parallel, the reciprocal of the total resistance of the system is equal to the sum of reciprocal of the resistance of resistors.

Potential difference across point A and B = V
Total current flowing between point A and B = I
Currents flowing through resistors R1, R2 and R3 = I1, I2 and I3 respectively.
We, know that,
I = I1 + I2 + I3 …….(i)
Since, the potential difference across R1, R2, and R3 is the same = V
According to Ohm’s Law,

In parallel combination, the potential difference across each resistor is the same and is equal to the total potential difference.

If two resistors R1 &R2 are connected in parallel then,

Heating Effect of Electric Current

When electric current is supplied to a purely resistive conductor, the energy of electric current is dissipated entirely in the form of heat and as a result, resistor gets heated.
The heating of resistor because of dissipation of electrical energy is commonly known as Heating Effect of Electric Current.
Some examples are as follows : When electric energy is supplied to an electric bulb, the filament gets heated because of which, it gives light. The heating of electric bulb happens because of heating effect of electric current.

Cause of Heating Effect of Electric Current:

Electric current generates heat to overcome the resistance offered by the conductor through which it passes.
Higher the resistance, the electric current will generate higher amount of heat. Thus, generation of heat by electric current while passing through a conductor is an inevitable consequence.
This heating effect is used in many appliances, such as electric iron, electric heater, electric geyser, etc.

Joule’s Law of Heating Effect of Electric Current

It states that the heat produced in a resistor is (i) directly proportional to square of current, H ∝ I²
It is directly proportional to resistance for a given current, H ∝ R
It is directly proportional to time for which current flows through the conductor, H ∝ t.
So, H = I²Rt
Heating effect is desirable in devices like electric heater, electric iron, electric bulb, electric fuse, etc.
Heating effect is undesirable in devices like computers, TV, refrigerators etc.
In electric bulb, most of the power consumed by the filament appears a heat and a small part of it is radiated in form of light.

Electric Fuse: It is a safety device that protects our electrical appliances in case of short circuit or overloading.

Electric Power:

The rate at which electric energy is consumed or dissipated in an electric circuit.
P = VI
P = I²R = V²/R
S.I. unit of power = Watt (W)
1 Watt = 1 volt × 1 ampere
Commercial unit of electric energy = Kilo Watt hour (KWh)
1 KWh = 3.6 × 10⁶ J
1 KWh = 1 unit of electric energy