What is current in electrical engineering ?

Here, we are going to study about electric current in electrical. After all what is this current in electrical? if we say in a simple way then flow of free electrons in a conductor or circuit. So let’s get to know more about current.

The rate of flow of charge in a conductor under potential difference is called electric current. The flow of current is shown in figure, where the copper strip has a large number of free electrons.

When voltage is apply, the free electrons start moving towards the positive terminal around the circuit. Because the free electrons negatively charged, This direct flow of electrons is called electric current.

The direction of current flow is caused by electrons ( in metals ) and The direction of current flow is opposite to the direction of electron flow.

Copper, aluminum are very good conductor so current or electricity flows easily in it. A current of one ampere flows in a conductor, It means that in one second 6.25 × 10¹⁸ electrons are entering from one end or exiting from the other end.

So there are two types of current alternating current (a. c.) and direct current (d. c.).

Alternating current

The current due to which such voltage flows repeatedly changes its direction by this we call it alternating current. We get the alternating current from the alternator

Direct current

The current which always flow in one direction is know as direct current. and We get the direct current from the generator.

 Read also this what is alternator in electrical

Unit of electric current

The S.I. unit of current is ampere (A) or coulomb/sec and it is represent by the symbol  ‘I’ and Electric current is scalar quantity.

What is ammeter? 

Ammeter is a device it is use for measure electric current in a circuit and it is connect in series in the circuit.

Measurement of current

The flow of free electrons ( or charge ) in a definite direction is know as  current. It is measure by the time rate of flow of charge through the conductor. If charge ‘q’ flows through the circuit for ‘t’ time then,  Electric current I = q/t

If the rate of flow of charge changes with time then the current flowing at any time ( instantaneous current ) is  i = dq /dt. Here dq is the small charge and it is passing through any cross-section of the conductor in less time dt.

If q = 1 coulomb and t = 1 second, then  ‘I’ = 1/1 = 1 ampere.

One ampere current is said to flow through the wire if one coulomb of charge flows through a cross-section in one second. If  ‘n’  electrons are passing through a cross-section of the wire in time ‘t’ .

Then,  I  =  q/t = ne/t  [ Where,  e =  −1.6 × 10⁻¹⁹ C  and n = 1,2,3 number of electrons]

Read also this what is resistance in electrical

ac and dc current difference

A. C.

1. AC means alternating current.
2. In alternating current voltage or current varies w.r.t time.
3. AC sources are hydroelectric power plants, thermal power stations, nuclear power station, generator.
4. AC can be converted to dc by using rectifiers.
5. The ac voltage can be stepped up and down by using a transformer.
6. In India ac has frequency of 50Hz.
7. In ac high voltage transmission and distribution of electricity is possible and it is cheap.
8. Large power rating motors can run by ac easily.

D. C.

1. DC means direct current.
2. In direct current voltage and current constant w.r.t. time.
3. DC sources are batteries, cells, inverters.
4. DC can be convert to ac using inverters.
5. It is not possible to Step up or down the dc voltage using a transformer.
6. Here frequency is equal to zero.
7. In dc high voltage transmission and distribution is costly.
8. In dc, large rating motors can not run.

Before knowing the formula of current, we need to know ohm’s law because from ohm’s law we will derive the formula of current.

What is a ohm’s law ?

Physical condition being an change the current through any conductor is directly proportional to the applied potential difference across it.

Mathematically,  V ∝ I

                            V = RI

                           R = V/I

What is the formula of electric current?

The electric current is the ratio of the potential difference and the resistance.

 From ohm’s law we get the formula of electric current 

V = RI

I = V/R .

So the formula of current is I = V/R

Where, I = Current and V = Potential difference and R is the Resistance.

State kirchhoff’s law

Sometimes we are faced with such a circuit which is very difficult to solve ( Like series and parallel combination ). And in such a circuit we cannot apply ohm’s law because it is impossible that’s why Gutsav kirchhoff’s  gave two laws to solve such a complex circuits.

So these two laws are kirchhoff’s current law (KCL) and kirchhoff’s voltage law (KVL).

Kirchhoff’s current and voltage law

Current law –

In open circuit, the algebraic sum of all the currents meeting at a point is equal to zero. 

Other wise, It can be stated that the algebraic sum of current entering a node must be equal to the algebraic sum of the current leaving the node. Consider five conductors carrying currents I₁, I₂, I₃, I₄ and I₅ and meeting at a point O as shown in figure.

Here I₁ and I₂ current are entering in AO and BO direction and I₁, I₂, I₃, I₄ and I₅ currents are leaving in OC, OD and OE direction.  Now assuming that current reaching at junction O are positive and current leaving junction O are negative 

Then, I₁ + I₂ + (−I₃ ) + (−I₄ ) + (−I₅ ) = 0 

         I₁ + I₂ − I₃ − I₄ − I₅ = 0

          I₁ + I₂ = I_{3 +} I₄ + I₅

Sum of incoming currents = Sum of outgoing currents

Voltage law –

The algebraic sum of voltages ( All voltage drops ) in any closed path of network that is traverse in a single direction is 0. And kirchhoff’s voltage law is also know as loop rule

In other way, In a closed circuit the algebraic sum of the product of current and resistance of different parts of loop is equal to the algebraic sum of the emf in the loop.

Σ V + Σ IR = 0

Σ E + Σ IR = 0

Where, E = emf and IR = Voltage drop 

 − V₁ − V₂ + iR₁ + iR₂ = 0 

= V₁ + V₂ = iR₁ + iR₂ 

Application of kirchhoff’s law

To solve the network, kirchhoff’s laws can be employed in the following ways.

Maxwell’s loop or mesh current method, Nodal voltage method and Branch current method.

Read also this What is the relation between torque and rotor power factor ? click here.

From the above discussion we have known about current in electrical, they are of two types AC and DC. Cooler, washing machine and motor all run on alternating current and the other hand direct current mobile, computer, electronic equipment and inverter all of them use direct current. 

Hope you like this concept, this one most important concept in electrical engineering, and basic thing you need to be clear, So hope this article clears your basics, Thank you.