Electric Current

Table of Contents

What is Electric Current?

The rate of flow of charge with time through any conductor is called as electric current. It is denoted by ‘I‘.

If ‘q’ charge crosses any conductor in time t, then

I = q/t ……………….(i)

If ‘dq’ be the variation in charge in time dt, then

I = dq/dt ……………….(ii)

Units of Current:

The S.I. unit of current is Ampere.

From (i)

1 Ampere = 1 coloumb/1 second

Current through a wire is said to be one Ampere, if one coloumb of charge flows through it in one second.
The C.G.S. unit of electric current is stat-ampere or e.s.u. of current.

From (i)

1 stat-ampere = 1 stat coloumb/1 second

The current through a wire is said to be one stat-ampere, if one stat coloumb of charge flows through it in one second. Also,

1 Ampere = 3 x 109 stat-ampere

Direction of Current:

By convention, the direction of flow of positive charge is taken as the direction of the current. This is called conventional current. It should be noted that electrons flow in a direction opposite to conventional current. It should again be noted that current is a scalar quantity.

Types of Current:

There are three types of current-

Steady Current:

STEADY CURRENT - Electric Current

It is that current whose magnitude does not change with time. It is as shown in figure.

Varying Current:

VARYING CURRENT - Electric Current

It is that current whose magnitude changes with time. It is as shown in figure.

Alternating Current:

Alternating Current - Electric Current

It is that current whose magnitude changes continuously with time and direction changes periodically. It is as shown in figure.


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