Electric current

Electric Current: The flow of electric charge is known as Electric Current, Electric current
is carried by moving electrons through a conductor.
By convention, electric current flows in the opposite direction to the movement of electrons.

Electric Circuit: Electric circuit is a continuous and closed path of electric current.

Expression of Electric Current: Electric current is denoted by the letter ‘I’. Electric current
is expressed by the rate of flow of electric charges. Rate of flow means, the amount of charge
flowing through a particular area in unit time.




If a net electric charge (Q) flows through a cross-section of a conductor in time t, then,




Where I is electric current, Q is a net charge and t is a time in second.

S.I. Unit of Electric Charge and Current: S.I. unit of electric charge is coulomb (C).
One coulomb is nearly equal to 6 × 1018 electrons. S.I. unit of electric current is ampere (A).
Ampere is the flow of electric charge through a surface at the rate of one coulomb per second.
This means, if 1 coulomb of electric charge flows through a cross section for 1 second, it
would be equal to 1 ampere.
Therefore, 1 A = 1 C/1 s

Small Quantity of Electric Current: Small quantity of electric current is expressed in
milliampere and microampere. Milliampere is written as mA and microampere as pA.
1 mA (milliampere) = 10-3 A
1 pA (microampere) = 10-6 A

Ammeter: An apparatus to measure electric current in a circuit.,

Charge: Like mass, the charge is the fundamental property of matter. There are two types of
charge
(i) Positive charge.
(ii) Negative charge.

, Positive and Negative Charge: The charge acquired by a glass rod when rubbed with silk is
called a positive charge and the charge acquired by an ebonite rod when rubbed with wool is
called negative charge.

Properties of Electric Charge:
(i) Unlike charges attract each other and like charges repel each other.
(ii) The.force between two charges varies directly as the product of two charges and inversely
as the square of the distance (r) between both charges (q1 and q2).




Where k is constant
S.I. unit of charge is coulomb (C).
1 coulomb = 1 ampere × 1 second.
1C = 1A × 1s
Thus, the quantity of charge which flows through a circuit when one ampere of current flows
through it in one second is known as a 1-coulomb charge.

Electric Potential and Potential Difference
Electric Potential: The amount of electric potential energy at a point is called electric
potential.
Potential Difference: The difference in the amount of electric potential energy between two
points in an electric circuit is called electric potential difference.
Electric potential difference is known as voltage, which is equal to the amount of work done
to move the unit charge between two points against static electric field.
Therefore, Voltage = 𝑊𝑜𝑟𝑘𝑑𝑜𝑛𝑒/𝐶ℎ𝑎𝑟𝑔𝑒
Voltage or electric potential difference is denoted by V’. Therefore, V = 𝑊𝑄
Where, W = Work done and Q = Charge
S.I. Unit of Electric Potential Difference (Voltage)and of electric potential difference is volt
and denoted by ‘V’ This is named in honour of Italian Physicist Alessandro Volta.

Since joule is the unit of work and Coulomb is the unit of charge, 1 volt of electric potential
difference is equal to the 1 joule of work to be done to move a charge of 1 coulomb from one
point to another in an electric circuit. Therefore
1V = 1Joule/1Coulomb = 1J/1C
1V = 1JC-1

Voltmeter: An apparatus to measure the potential difference or electric potential difference
between two points in an electric circuit. It is always connected parallel in an electric circuit
because of its very high resistance.

Galvanometer: It is a device to detect current in an electric circuit.