Electric Current: Meaning, Difference and Formula

Key Concepts

• Electric Current
• Ampere
• Ammeter
• Static charge

Introduction: 

Earlier people relied on fire for light, warmth and cooking. Now a days at the flick of a switch everything is possible. This is possible because of electric current. In this section you will read about electric current, its SI unit, Ampere and the instrument used to measure the electric current.  

Explanation: 

Electric Current: 

An electric current is the rate of flow of electric charges in an electric circuit.  It is the amount of charge passing a point in a conductor every second. Its direction in the electric circuit is taken to be the same as that of the convectional current. 

Mathematically,  

Where,  

I = current flowing through wire 

Δ Q∆ Q

= amount of charge 

Δ t=time taken∆ t=time taken

You have read about static electricity. Static electricity and current electricity are different. Static electricity is because of the charges that are stationary whereas electric current is because of the flow of electrons.  

The difference between static electricity and current are;

Ampere: 

After the French physicist André-Marie Ampère, SI unit of electric current is Ampere (A).  

A few prefixes of Ampere are used as multiples and sub-multiples of SI unit are microampere, milliampere, ampere and kiloampere.

Ammeter: 

Ammeter is a device which is used to measure the current in a circuit. It is always connected in series in a circuit. A multimeter also measures the current in the circuit when connected in series in A, mA and μA. 

The symbol of ammeter when connected in an electric circuit is 

It has both positive and negative terminal. The red one is positive and black is negative. If both terminals are black, the one with 0 A is positive and the range terminal is negative. 

Coulomb: 

Coulomb is the SI unit to measure current. It is equal to the amount of charge transferred in one second by a steady current of one ampere. 

Mathematically,   

Q = I.t  

1 C = 1 A. 1s  

1 Coulomb has 6.28 x 10¹⁸

electrons in it. 

Questions and answers 

Question 1: Two batteries are connected in a circuit as shown. What is the impact on the electric current? 

Answer: 

Since the amount of the electrons passing the conductor at a point will increase when two batteries are connected, hence the electric current will increase. 

Question 2:  Ruhana has an ammeter which she wants to place in the given circuit. How should she place it to get the reading.  Also, on placing it in the circuit the ammeter shows a reading of 0.5 mA. How much Ampere of current did the ammeter record. 

Answer: 

The ammeter needs to be placed in series in the circuit.

Ammeter reading = 0.5 mA 

We already know that  

1 milliampere = 1 mA =1× 10−31× 10⁻³A

So 0.5 milliampere  

= 0.5 mA  

=0.5×10−30.5×10⁻³A

summary

• Electric current is the amount of charge passing a point in a conductor every second. I = ΔQ / Δt
• It is measured in Ampere (A). 1A= 1C / 1s
• Its direction is taken from positive terminal of the battery to the negative terminal same as the convectional current.
• It is measured using the instrument “Ammeter”, which is connected in series in the circuit.