Electric Current

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What is electric current

Electric current is the flow of electric charge through a conductor. e.g. in a torch, the cells provide the flow of charge or an electric current through the torch bulb to glow.

Electric current is defined as the rate of flow of electric charge through a conductor. If Q amount of charge flows through a conductor in time t, then

Electric current I = Charge (Q)/Time (t) = ne/t

Where, n = number of electrons flowing through the conductor

e= electronic charge = 1.6×10-19 C

The SI unit of electric current is ampere (A) in honor of French scientist Andre-Marie Ampere. It is a scalar quantity.

When 1 coulomb of charge flows through any cross section of a conductor in 1 second then the electric current flowing through it is said to be 1 A.

1 ampere = 1 coulomb/1 second ⇒ 1 A = 1C/1s

Small units of current are milliampere (1mA = 10-3A) and microampere (1μ = 10 -6A). The direction of flow of positive charges is taken to be the direction of electric current. Conventianally, the direction of electric current is taken as opposite to the direction of the flow of electrons.

  • The basic difference in electricity and electrostatics is that the electricity deals with moving charge (flow of charge) while the electrostatics deals with the stationary charges.

Types of Electric current

According to its magnitude and directionn, electric current is of two types

  1. Direct current (DC) An electric current whose magnitude and direction do not change with time, is called direct current. e.g., a cell, battery or DC dynamo are the sources of direct current.
  2. Alternating Current (AC) An electric current whose magnitude change continuously and direction changes periodically, is called alternating current. e.g., AC dynamo is the source of alternating current.

Current Density

The current density at a point in a conductor is defined as the amount of current flowing through per unit area of cross-section of the conductor provided the area is held in a direction normal to the current.

Current density =Electric current/Area of cross section

The SI unit of the current density is ampere/metre² and it is vector quantity.

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