**What is Electricity? – Definition and S****ome Electrical Related Terms**

**Introduction**

**Electricity** is the greatest invention of science. It is very important in our daily life.** Electricity** is the form of energy through which we can use it in the form of light, heat, and power to run small and heavy machines in the workplace.

It illuminates our homes, street,s, etc. In industries, it plays a very important role. Heavy machines run by using electricity. We find electricity everywhere. You cannot expect anything without electricity.

**What is Electricity?**

**Electricity** is the form of energy that results due to the existence of charged particles **(electrons)** which may either** statically** in the form of accumulation of charged particles (electrons) or **dynamically** as current **(flow of electrons).**

So there are two types of electricity **static** and **dynamic.**

We know that all matters such as solids, liquids, and gases are made of very small particles called molecules. Molecules are further subdivided into small particles called atoms. In other words, we can say that molecules consist of two or more atoms or groups of atoms that are bounded by a Covalent bond (chemical bond).

These atoms are described in the shape of circles that have a nucleus at the center. Each nucleus has protons and neutrons surrounded by one or more concentric circles called shells or levels in which electrons revolve around the nucleus.

Protons and neutrons have approximately the same masses (1.67 x 10^{ -24} grams). Electrons are much smaller than protons having masses of about 9.11 x 10^{-28} grams or about 1/1800 of an atomic mass unit. So a nucleus contains protons and neutrons having a huge amount of masses at the center of an atom.

Protons have positive charge carriers, neurons have no charges or are changeless and electrons have negative charge carriers.

An atom contains an equal number of protons and electrons. Therefore in normal conditions, an atom has no charge or remains neutral. As the nucleus contains protons and neutrons, so overall nucleus has a positive charge carrier.

Electrons have a negative charge of – 1.602 x 10 ^{-19} C and protons have a positive electric charge of +1.602 X 10 ^{-19 C}

An electron close to the nucleus is strongly attracted to a proton. When there is a weak bond or the outermost electron loses its bond, electricity is developed, or the shifting of an electron from one atom to another atom is called **electricity**.

**What is an electric charge?**

**In terms of force**

An Electric charge is a force experienced by moving an electron when it is placed in an electric or magnetic field.

**In electric field**

F=q E or q=F/E, q= electric charge particle =No. of electrons=ne

Where E= electric field

F= force experienced by electric charge

**In magnetic field**

**According to Lorentz force law,**

F=q v x B = q v B Sinθ where, θ is the angle between the velocity of the moving charged particle and the magnetic field, v= velocity of the moving charged particle, B= Magnetic field

Static electric charge is associated with an electric field and dynamic electric charge is associated with a magnetic field.

The combination of an electric and magnetic field is described as an electromagnetic field. The interaction of one or more charges generates electromotive force.

**In terms of current and time**

It is the product of current and time.

Hence Q= I.t , where I= current and t= time

It is measured in amp-hour; 1 AH=3600 coulombs.

The unit of charge in the SI unit is coulomb and represented as C

**Some electrical quantities used in electricity**

**Electromotive force (emf)**

It is the force that is responsible for the flow of electrons in a closed circuit. Its unit is volt (V).

**Potential difference (P.D)**

It is the difference in voltage between two points of conductors required to drive the current between them. It is measured by a voltmeter. It is also called voltage and is measured in volt V.

**Current**

Current is defined as the flow of charges or the flow of electrons in any conductor. It is also defined as the rate of flow of charge in unit time.

I=d q/dt=Q/t=ne/t, ne= no of electrons.

In an open circuit, there is an increased voltage, and the flowing of current stops. In a short circuit, heavy current flows but voltage decreases.

Unit: Ampere

It is measured by an ampere meter

One important thing about current is that it does not flow through the conductor unless there is a potential difference. Electric current flows from higher potential to lower potential if the circuit completes its path.

**Frequency **

It is the number of cycles per second.

f=1/T, where T= time period

SI unit is hertz.

**Also Read:- basic electrical definitions and laws**

**There are two types of currents**

**Alternating current **

The current or voltage that changes periodically or alternates its directions and magnitudes every time is called alternating current (AC).

In other words, current or voltage changes its direction in alternate positive and negative half-cycles. It has both magnitude and direction but does not obey the vector addition. So it is a scalar quantity.

Alternating current (A.C ) has a frequency (f). It includes resistance, inductance, and capacitance. In an AC circuit, there is some angle between voltage and current. So the power factor is lagging, leading, or unity.

**Also Read:- what is power factor**

**Direct current **

Current flows in unidirectional are called direct currents. It does not change its direction. Direct current does not flow in a reverse cycle. No. of cycle per second is zero. Hence in direct current (D.C), frequency is zero or absent.

AC and DC.

Direct current has only resistance. In DC, the current is in phase with voltage i.e. there is no angle between voltage and current. So power factor is unity.

**Resistance**

Resistance is defined as the property of substances that oppose the flow of current (or electron). It is represented by R.

The unit of resistance is the ohm (Ω).

Its biggest unit is Mega ohm (10^{6}) and the smallest unit is micro–ohm (10^{-6}).

R is directly proportional to the length of the conductor and inversely proportional to the cross-section area of the conductor.

R= ρ L/A, where ρ (rho) = constant for a material called specific resistance or resistivity or the coefficient of resistance.

Resistance of pure metal increases linearly with increased temperature;

R_{ t}= R _{0} (1+ α∆ t), where α= temperature coefficient of resistance. ∆t=temperature difference

**Key points:**

The resistance of a conductor depends upon the following factors:

- It varies directly with the length of the conductor
- It Inversely varies to the Cross-section area of the conductor
- It depends on the nature of the conductor
- It depends on the Temperature of the conductor

**Inductance**

It is the property of a coil in which emf is induced due to flux linked with the coil changes.

According to Faraday’s law of electromagnetic induction

e= d Ψ/dt=N d ф/dt where ф α i

e= emf induced, N= number of turns in the coil, Ψ=Nф=flux linkage with the coil, t= time in second, i=current in ampere.

Inductance is the ability of a coil to store energy in form of a magnetic field that is created due to the flow of current.

The inductance of a coil is represented by L.

The unit of inductance is Henry (H).

**Capacitance**

It is defined as the amount of electric charge stored in the conductor due to the voltage applied to it.

Hence C=Q/V, where C= capacitance of a capacitor, Q= electric charge, V= voltage (in volt)

Unit of capacitance is Farad (F)

A Capacitor is a device that stores energy in the form of an electric field

Energy stored in capacitor= 1/2 C V ^{2}

**Ohm’s law**

This law gives the relationship between voltage, current, and resistance.

According to this law, the ratio of potential difference (V) between two points of a circuit (or voltage across a conductor) to the current flowing through that circuit is constant, provided that all physical conditions and temperatures remain constant.

So, V/I=R, where R is constant called resistance

Or

This law states that in any closed circuit, a current is directly proportional to the applied voltage and inversely proportional to the resistance of a circuit.

Hence, I ∝V and I ∝ 1/R

Or, I =V/R or V= IR

Some drawbacks of Ohm’s law:-

As you know that Ohm’s law is applicable only if all physical conditions and temperatures remain constant.

So it is not applicable for:

- Light bulb as the temperature of a filament of a bulb increases with current increased.
- For arc lamp
- For electronic valves.
- For metals that are heated by the current to a high value.
- For a gas-filled tube in which ions are generated with the passage of current.

**Kirchhoff’s law**

Kirchhoff’s law is very helpful for determining equivalent resistance and the current flowing in various circuits in a complex network.

**Kirchhoff’s current law(KCL)**

This is also called Kirchhoff’s 1st law or Kirchhoff’s current law (KCL). This law is applicable to currents at a junction or node in a circuit.

This law states that the sum of currents at any junction of the network is zero. In other words at a node or at a point, the sum of incoming current is equal to the sum of outgoing current or current flowing toward the point is equal to the total current leaving away from the point. This is the consequence of charge conservation.

**Kirchhoff’s voltage law(KVL)**

This is also known as Kirchhoff’s second law or Kirchhoff’s voltage law (KVL). This is a consequence of charge conservation and follows the conservation of energy law.

In any closed circuit, the algebraic sum of Potential drops (IR) is equal to the sum of impressed emf across other components in the same loop, or the algebraic sum of all the voltage around a closed loop is zero

Or,

**Kirchhoff’s second law or voltage law states that:-** The net electromotive force around a closed loop is equal to the sum of voltage (potential) drops around a closed loop.

If we count the moving charge in the closed-loop and battery as the source then

Total energy by the charges=corresponding loss in energy through resistance, inductance, and capacitance

Mathematically,

ΣV+Σ IR=0

Application:-

- It helps to solve the calculation of unknown vintages and currents in the complex network
- The analysis and simplification of the closed-loop circuits become easy.

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