Electric Current – Definition, formula & unit

Last updated on April 16th, 2021 at 09:58 am

If two charged bodies are connected by a metallic wire, electrons start flowing from the body having more electrons (negatively charged body), to the body with less electrons (positively charged body). An electric current is produced by the flow of electrons. Thus we can say that current flows due to the motion of charges. The rate of flow of charge gives the magnitude of the current. Thus we can define Current as the rate of flow of charge across the cross-section normal to the direction of flow of current.

Electric Current Definition | What is electric current?

Current is defined as the rate of flow of charge across the cross-section normal to the direction of flow of current.

Electric Current Formula

Say, charge Q flows through the cross-section of the conductor in a time duration t.

Then the current flowing through the same conductor is expressed as:

Current (I) = Charge (Q) / time duration (t)
=> I = Q/t ………………………………………..(1)

Electric current equation in terms of charge of electron | formula for electric current in terms of e

In metal conductors, current flows due to the movement of electrons. An electron carries a negative charge equal to -e, where e = 1.6 x 10 ^(-19) coulomb. Now say, n number of electrons flow through the cross-section of the conductor in time t to constitute the electric current.

Then total charge passed in time t = Q = n x e
Now from equation (1) we get, I = Q/t = (n e) / t ……………(2)

From equation (1) given above, we will get the unit of current.
Equation (1) says that, Current= Charge / Time Duration
So unit of current = unit of charge / unit of time ————-(3)

In SI the unit of charge is Coulomb and the unit of time is second.

So the SI unit of current is Coulomb/second.
This Coulomb per second is also known as Ampere. Its Symbol is A.
[The ampere is named in honor of Andre Marie Ampere, the french Physicist who contributed in many ways to understand electricity.]

Ampere

Ampere is the SI unit of Current.

Therefore we can say that when 1 A current flows through a conductor that means 1 Coulomb charge flows in a time duration of 1 second.

Common measuring instrument of current

The electric current in a circuit is measured by an instrument called the ammeter. Ammeter is connected in series with the element or the circuit (the current through which is to be measured)

Numerical problem (sample)

Q>
6 x 10 ^17 number of electrons pass through an area per minute. What is the electric current?

n = 6 x 10 ^17 = number of electrons
e = charge of electron = 1.6 x 10 ^ (-19) Coulomb
t = time duration = 1 min = 60 s

We will use this formula:
I = Q/t = ne / t

Putting all the values and after calculating we get,
I = 1.6 mA.

This electricity class notes is apt for
1) class 9 ICSE
2) class 10 ICSE
3) CBSE: electric current class 10