# Electric Current

**Electric Current:** The flow of electric charge is known as electric current. Electric current is carried by moving electrons through a conductor.

Fig: Conventional Flow of Electric Charge

By convention, electric current flows in opposite direction to the movement of electrons. As shown in this figure, electron flows from negative terminal to positive terminal. As a result, electric current flows from positive terminal to negative terminal.

## Electric Circuit

**Electric Circuit:** Electric circuit is a continuous and closed path of electric current. If the circuit is complete, i.e. not broken, it is called a **closed circuit.** If the circuit is not complete, i.e. broken, it is called **open circuit.**

### Expression of Electric Current

Electric current is denoted by 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 conductor in time t, then:

`text(Electric Current) (I)=(text(Net charge) (Q))/(text(Time) (t))`

Or, `I=Q/t`

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

#### SI unit of Electric Charge and Current:

SI unit of electric charge is coulomb (C).

One coulomb is nearly equal to `6 xx 10^18` electrons. SI unit of electric current is ampere (A). Ampere is the flow of electric charges 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 μA

1mA (milliampere)`= 10^(-3)` A

1μA(microampere)`=10^-6` A

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

Example 1: Find the amount of electric charge flowing through the circuit if an electric current of 5 A is drawn by an electric appliance for 5 minute.

**Solution:** Given, electric current (I) = 5 A

Time (t) = 5 minute `= 5 xx 60 = 300` s

Electric charge (Q) =?

We know, `I = Q/t`

Or, `Q = I xx t`

Or, `Q = 5 A xx 300 s = 1500 C`

Example 2: If a current of 2 ampere is drawn for 1 hour through the filament of a bulb, find the amount of electric charge flowing through the circuit.

**Solution:** Given, electric current (I) = 2 A

Time (t) = 1 hour `= 1 xx 60 xx 60 s = 3600 s`

Electric charge (Q) =?

We know that `Q = I xx t`

Therefore, `Q = 2 A xx 3600 s = 7200 C`

Example 3: In how much time 6000 coulomb of electric charge will flow, if an electric current of 10 A is drawn through an electric motor?

**Solution:** Given, electric charge (Q) = 6000 C

Electric current (I) = 10 A

Time (t) = ?

We know, `I = Q/t`

Or, `t = Q/I`

Or, `t = (6000 C)/(10 A) = 600 s`

Or, `t = 10` min

Example 4: If an electric charge of 900 C flows through an electric bulb for half an hour, find the electric current drawn by the filament.

**Solution:** Given, electric charge (Q) = 900 C

Time (t) = Half an hour = 30 m `= 30 xx 60 = 1800 s`

Electric current (I) =?

We know, `I = Q/t`

Or, `I = (900 C)/ (1800 s) = 0.5 A`

Example 5: If an electric charge of 1500 C flows through an electric iron for 5 minute, find the electric current drawn by filament of electric iron.

**Solution:** Given, electric charge (Q) = 1500 C

Time (t) = 5m `= 5 xx 60 = 300 s`

Electric current (I) =?

We know, `I = Q/t`

Or, `I = (1500 C)/(300 s) = 5 A`

## Summary

**Electric Current:**Flow of electric charge is called electric current, and its SI unit is Ampere.**Electric Circuit:**The path through which electric current flows. It can be open or closed.