Electric Current

An ordered motion of charged particles in a definite direction is termed as electric current Its magnitude is determined by the amount of net charge flowing through a cross section, perpendicular to the direction of the flow in unit time. Electric Current can be calculated by using the relation:

$large I=frac{q}{t}$ ,

Where I = current flowing

q= charge

t= time

The SI. unit of electric current is ampere (A) named in the honour of a French Andre Marie Ampere. Electric Current is a scalar quantity.

We consider Ampere is a fundamental unit and Coulomb is derived from ampere, because electric current was discovered first and the phenomenon that Electric current is because of flow of electrons was discovered later.

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 ampere.

$1 ;ampere= frac{1 ;coulomb}{1; sec}Rightarrow 1;A=frac{1;C}{1;s}$

The smaller unit of current is milli ampere (1 mA = 10^-3 A) and micro ampere (1 $mu$ A = 10^-6A)

Illustration: A current of 150 mA flows through a circuit for 2min. Find the amount of charge that flows through the circuit.

Solution: Given, Current, $large dpi{100} large I=150mA=150times10^{-3}A$

Time, $large t=2min=2times60=120s$

Amount of charge, q = ?

We know that, $large q=Itimes t$

$large Rightarrow ;;q=150times10^{-3}times120$

$large Rightarrow ;;q=18C$

So, 18 C of charge flows around the circuit.

Illustration: If we observe that 20 C of net charge flows across a cross section of a current carrying wire in 4 seconds. Find the value of current?

Solution: Net Charge (q) = 20C and time(t) = 4sec

$large Electric ;Current;(I)=frac{Charge(q)}{Time(t)}$

$large Electric ;Current=frac{20}{4}=5A$

Direction of Current

In a circuit the direction of flow of current is taken from positive terminal to negative terminal. This is the conventional direction of current. The actual; direction of current is from negative terminal to the positive terminal. As we know the electrons are the charge carrier and they are negatively charged so they will be attracted towards the positive terminal hence the actual direction of flow will be from -ve terminal to positive terminal.

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Sample Questions

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