Class 10 Physics



Electricity

Electric Current and Electric Circuit

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 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 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.


flow of electric charge

Fig: Conventional Flow of Electric Charge

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 15000 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`