Table of Contents

## What is Electric Current?

The rate of flow of charge with time through any conductor is called an 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 10 ^{9} 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:**

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

**Varying Current:**

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

**Alternating Current:**

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