Friction is one of the ways to prove that the production of charge is possible. When charges flow, it results in the production of electricity. Let us learn about friction.

Friction is produced when two bodies rub or slide against each other. Take, for instance, a glass rod. When you rub it with silk, friction is produced. It results in the rise of charge. The SI unit of charge is Coulomb. It was named after a French engineer and scientist, Charles Augustin de Coulomb.

There are two types of electric charges. They are:

1. Positive charge
2. Negative charge

The symbol used to denote charge is Q and the unit in which it is measured (Coulomb) is denoted by C. Various experiments and studies proved that the same type of charges repel each other. And materials with opposite electric charges attract each other.

Electric charges create a field around them known as the electric field. An electric charge is directly proportional to the number of electrons and the magnitude of the charge on the electron.

Q = n \( \times \) qₑ 

where n = Number of electrons

qₑ = charge of the electron that is equal to 1.63 \( \times \) 10⁻¹⁹.

As per Coulomb's law, the force between two charges is directly proportional to the product of the magnitude of the charges and inversely proportional to the square of the distance between them.

F = K (q1 x q2)/r²

F = Force

K = Coulomb’s constant = 8.988 \( \times \) \( 10^{9} \)

q1 and q2 are magnitudes of the charges

r is the distance between q1 and q2

Substances can be differentiated depending upon their ability to conduct electricity. The two types of substances, by this classification, are as follows:

1. Conductors are those substances that allow the current to easily pass through them since they have free mobile electrons. Some examples of conductors are copper, aluminium, silver, and gold.
2. Insulators are those substances that do not allow current to easily pass through them, as they do not have free mobile electrons. Some examples of insulators are glass and plastic.

Types of electricity

There are two types of electricity. 

1. Static electricity
2. Current electricity

Static electricity is a type of electricity developed due to the presence of charges, but they do not flow. Take, for example, charges developed by rubbing the glass rod with silk.

Current electricity is a type of electricity that is produced when charges are in motion. Take, for example, the electricity that is used in our homes.

It is defined as the work done to move a positive charge from infinity to a certain point in an electric field of another charge.
For example, a unit of positive charge Q1 is at a point at infinity, and we try to bring it to point B, which is in the electric field of a charge Q2. The work that will be required to do this is called electrostatic potential.

Potential difference

It is defined as the work done to move a charge between two specified points. The unit used to measure it is volt.

In other words, the potential difference can be defined as 1V when one joule of work is done to move 1C of charge from one point to another. The instrument used to measure potential difference is called a voltmeter. It is always connected in parallel in a circuit.

 

It is the rate of flow of electric charge. A conducting material is ideal for the flow of electric charges. The SI unit of electric current is Ampere and denoted by the symbol A.

1A of electric current is equal to 1C of charge flowing through a cross-section of area per second. A useful instrument to measure the current is an ammeter. It offers lower resistance, and therefore it is connected in series in a circuit as the current remains constant.

Electric circuits

An electric circuit can be defined as a path, made up of electric components, through which electric current flows from one point to another.

There are two types of electric circuits. These are:

1. Open circuit
2. Closed electric circuit

Open electric circuit: There is no electric current flowing in an open electric circuit.

Closed electric circuit: In a closed electric circuit, all the components are joined together in such a way that continuous current flows through it.

Some important electronic instruments are as follows:

Rheostat: It is used to provide variable resistance in a circuit.

Galvanometer: It is used to detect small amounts of current as it provides very little resistance.

This law is a generalisation made by a scientist called Georg Ohm. He did so based on his experiments. He explains that the current flows through the circuit at a constant temperature. The current is directly proportional to the potential difference which is applied at the ends of the conductor.

V= I \( \times \) R, where V is the potential difference, I is the current flowing and R is the resistance of the conductor.

Joules heating effect

During the flow of electric current, the electrons move and collide. Thus, heat is produced. This production of heat depends on temperature, current, and resistance.

H=I² \( \times \) R \( \times \) T (H = heat produced, I = current flowing, R = resistance and T = temperature)

This is known as the joule's heating effect.

It is significant to highlight that for heating devices, nichrome wire is used due to the following properties:

1. It doesn't burn at high temperature
2. It has high resistance.
3. It has a high coefficient.

Power

Do you wonder what power means every time you read it on an electric appliance?

We can easily define it as P = W/t (P = Power, W = Work and t = elapsed time). It refers to the rate at which the work is done.

It is the biggest protection against fire in case a short circuit occurs in an electrical circuit, resulting in a fire. An electric fuse acts as a safety device. When excessive current flows through a circuit, the fuse wire breaks and stops the flow of current. Fuse wire has a low melting point and is made from lead and tin.

Exercises of NCERT solutions for Class 10 Electricity

1. What does an electric circuit mean?

2. Define the unit of current.

3. Calculate the number of electrons constituting one coulomb of charge.

4. Name a device that helps to maintain a potential difference across a conductor.

5. What is meant by saying that the potential difference between two points is 1V?

6. How much energy is given to each coulomb of charge passing through a 6V battery?

7. On what factors does the resistance of a conductor depend?

8. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?

Answers to NCERT solutions exercises for Class 10 Electricity

1. An electric component with a continuous closed path is called an electric circuit. Electric current flows through it.

2. It is ampere. It refers to the flow of one coulomb of charge in one second.

3. Charge of an electron = 1.63 \( \times \) 10⁻¹⁹C

Charge quantization, Q = n \( \times \) qₑ

After substituting the values, we get 6. 25 \( \times \) 10¹⁸.

4. To maintain a potential difference across a conductor, a battery is a useful device.

5. The potential difference between the two points is 1V when the following situation is true: 1J work is done to move a charge of 1C

6. Potential difference, V = W/Q

So, W = V \( \times \) Q

Substituting the values, we get

W = 6V \( \times \) 1C = 6 J

Thus, 6J energy is needed to pass through a 6V battery.

7. The resistance depends on the temperature, cross-sectional area, length, and nature of the conductor.

8. Resistance, R = ρ l/A 

where,

ρ= resistivity, l=length, A =cross-section

Thus, we know that the cross-section of the wire is inversely proportional to the resistance. It means that current flows easily via thick wire.

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