CBSE Class 10 Science Electricity Notes

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ELECTRICITY

Electricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena such as lightning and static electricity, but in addition, less familiar concepts such as the electromagnetic field and electromagnetic induction.

Electric charge

Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces. Electric charge is conserved, additive and quantised. The S.I. unit of electric charge is ‘C’ coulomb. Any other charged body will have a charge Q

Q = ne

where n is the number of electrons and e is the charge on electron = 1.6 x 10^–19 coulombs. 

Electric current

Electric current is a flow of electrons in a conductor such as a metal wire. Electric current is expressed by the amount of charge flowing through a particular area in unit time. In other words, it is the rate of flow of electric charges. In circuits using metallic wires, electrons constitute the flow of charges. However, electrons were not known at the time when the phenomenon of electricity was first observed. So, electric current was considered to be the flow of positive charges and the direction of flow of positive charges was taken to be the direction of electric current. Conventionally, in an electric circuit the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges. The magnitude of electric current in a conductor is the amount of electric charge passing through a given point of conductor in 1 second.

I =Q/t

S.I. unit of electric current is ‘A’ (Ampere).

The electric current is expressed by a unit called ampere (A), named after the French scientist, Andre-Marie Ampere (1775–1836).

One Ampere

When 1 coulomb of charge flows through any cross-section of a conductor in 1 second, the electric charge flowing through it is said to be 1 ampere. Smaller unit current is milliampere(mA) and microampere( A)

1 mA = 10^–3A

1 μA = 10^–6A

An instrument called ammeter measures electric current in a circuit. It is always connected in series in a circuit through which the current is to be measured. The direction of electric current is from positive terminal to negative terminal through the electric circuit. 

1. What does an electric circuit mean?

Ans. An electric circuit consists of electric devices, switching devices, source of electricity, etc. that are connected by conducting wires.

2. Define the unit of current.

Ans. The unit of electric current is ampere (A). 1 A is defined as the flow of 1 C of charge through a wire in 1 s.

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

Ans. One electron possesses a charge of 1.6 × 10−19 C, i.e., 1.6 × 10−19 C of charge is contained in 1 electron.

Potential difference

Potential difference, VA – VB between two points A and B is the work done per unit charge in taking a charge from B to A.

Potential difference, re VA is potential at point A, VB is

potential at point B and S.I. unit of potential is volts (V), named after Alessandro Volta (1745–1827), an Italian physicist.

Electric Potential

Electric Potential at a point is defined as the work done per unit charge in bringing a charge from infinity to that point.

The potential difference is measured by means of an instrument called the voltmeter. The voltmeter is always connected in parallel across the points between which the potential difference is to be measured.

One volt: The potential difference between two points is said to be 1 volt if 1 joule of work is done in moving 1 coulomb of electric charge from one point to the other. Electrons always flow from lower potential to higher potential.

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

Ans. A source of electricity such as cell, battery, power supply, etc. helps to maintain a potential difference across a conductor.

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

Ans. If 1 J of work is required to move a charge of amount 1 C from one point to another, then it is said that the potential difference between the two points is 1 V.

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

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