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Electricity

Electric potential

So, by now you must have understood electric potential and potential difference.

Let us define these two for you −

  • Electric potential of a point in an electric field is defined as the work to be done to move a unit positive charge from infinity to that point.

  • Potential difference between two given points in an electric field is defined as the amount of work to be done to move a unit positive charge from one point to the other.

Potential difference (V) =

Do you know?

The SI unit of electric potential is volt (V), named after the great physicist, Alessandro Volta (1745−1827).

A chemical reaction within a cell develops a difference in potential between both its terminals. When a cell is connected to a circuit, the potential difference causes the charge to flow and hence, the current is flowing through the circuit.

If we substitute the SI units of work done [i.e., Joule (J)] and charge [i.e., coulomb (C)] in the following relation, we get

V =

1 V =

Hence, we can define potential difference between two points as 1 J of work that is required to move 1 C of charge between two points.

  • The potential difference between two points is measured with the help of a voltmeter. For this purpose, it is connected across the points from where the potential is to be measured.

Do you know?

We can get an electric shock if we touch a naked live wire.

Electric current tends to flow due to the potential difference that exists between the Earth and a wire (as the wire acquires a positive value). Therefore, when we touch a naked live wire, our body provides the current a bridge or link to flow from high potential (wire) to zero potential (Earth) via our body. This flow results in an electric shock, which can prove to be fatal.

Do you know?

Birds sitting on live wires do not get electrocuted.

Potential difference is a must for current to flow. Birds do not get electrocuted while sitting on live transmission wires because their bodies do not provide a bridge or link for the electrons to flow. The potential of a bird’s body is zero before coming in touch with a wire. When a bird sits on a wire, its body potential rises and becomes equal to the potential of the wire. If a person standing on the ground touches the bird, then both will get an electric shock. This is because the person’s body would provide a link for the electrons to pass on to the Earth.

 

Electricity requires a link to flow from cells. Do you know how electricity flows through an electrical circuit? What constitutes a current in the circuit?

Electric charge

The distribution of charge in a body is measured in coulombs. The quantization of charge requires that a charge on a body always remain the integral multiple of charges in an electron. Therefore, we have the relation

Q = ne

Where, Q is the charge on the body

n is the number of electrons

e is the charge on electrons (1.6 × 1019)

The SI unit of electric charge is coulomb, denoted by the letter ‘C’.

Number of electrons in 1 C of charge

Total charge possessed by one electron = 1.6 × 10−19 C

i.e., 1 electron = 1.6 × 10−19 C

⇒ 1 C = electrons

Or, 1 C = 6.25 × 1018 electrons

Hence, we can say that one coulomb of electric charge contains 6.25 × 1018 electrons.

Electric current (Flow of charges)

The directed flow of negative charges (i.e. electrons) through a wire is called an electric current. A current is said to be flowing if a closed link has been provided for the electrons. This link is called the electric circuit. An electric circuit provides a continuous path for the el...

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