Electricity : Basics

 

ELECTRICITY:

Flow of electrons through a conductor produces electricity. Electrons create charge. Charge is directly proportional to number of electrons.
Precisely the flow of free valence electrons Valence electrons are the electrons on the outer orbits of an atom.

The three important and basic terms of electricity are,

• Voltage is the difference in charge between two points. Unit : Volts (V)
• Current is the rate at which charge is flowing. Unit : Amps (A)                                              Higher the number of electrons higher will be Amps
• Resistance is a material’s tendency to resist the flow of charge (current). Unit : Ohms (Ω). Depends upon the bond strength between nucleus and the valence electrons and also depends on the availability of free valence electrons.

POWER

Electric power is the rate at which electrical energy is transferred by an electric circuit.

Unit: Watt (W).

ELECTRIC ENERGY

Electric energy is defined as the capacity to do work. Unit: watt hour (Wh) or kilowatt hour (kWh).

1 kWh is known as one unit of electric energy.

E = P . t

VOLTAGE

Voltage or potential difference potential difference is the work done in moving a unit positive electric charge from one point to another in an electric circuit.

ELECTRIC CURRENT

The current is defined as the rate of flow of charges across any cross sectional area of a conductor. It is caused by drift of free electrons through a conductor to a particular direction.

I = q / t

CURRENT DENSITY

Current density at a point is defined as the quantity of charge passing per unit time through unit area, taken perpendicular to the direction of flow of charge at that point.

J = I / A

OHM’S LAW

At a constant temperature, the steady current flowing through a conductor is directly proportional to the potential difference between the two ends of the conductor.

V ∝ I

V = IR

RESISTANCE OF A CONDUCTOR

The resistance of a conductor R is directly proportional to the length of the conductor l and is inversely proportional to its area of cross section A.

R ∝ l / A

R = (ρ.l) / A

RESISTIVITY & CONDUCTIVITY

The electrical resistivity of a material is defined as the resistance offered to current flow by a conductor of unit length having unit area of cross section.

ρ = (R.A) / l

The reciprocal of electrical resistivity, is called electrical conductivity.

σ = 1 / ρ

RESISTOR

Resistor is an electronic element which limits the current passing through it. The resistance of an element denotes its ability to resist the current flow through it. Unit: ohm (Ω)

COLOUR CODING

The value of resistor can be found using its colour code.

0	Black	B
1	Brown	B
2	Red	R
3	Orange	O
4	Yellow	Y
5	Green	G
6	Blue	B
7	Violet	V
8	Grey	G
9	White	W

For example,

·        Resistor colour code: Red, Red, Brown

Colour code value: 2, 2, 1

⇒ 22x10¹ = 220 Ω

·        Resistor colour code: Brown, Black, Red

Colour code value: 1, 0, 2

⇒ 10x10² = 1000 Ω = 1KΩ

 FORMULAE:

• Voltage across the resistor,                                                                                                              V = IR
• Current through Resistor,                                                                                                                I = V / R
• Resistors in Series,                                                                                                                          R = R1 + R2
• Resistors in Parallel,                                                                                                                         
  
• Voltage Divideres:                                                                                                                             

Resistors in Series

Resistors in Parallel

DC Voltage Divider

TYPES OF RESISTORS 

1) Carbon Resistor
2) Film Resistor
3) Wire wound Resistor

RESISTOR APPLICATIONS

1) LED Current Limiting
2) Voltage Dividers
3) Pull-Up Resistors

CAPACITOR:

A capacitor is a passive electronic component that stores energy in the form of an electrostatic field. Capacitance is the ability to store electrical energy. Unit: farad (F). Symbol: C

The capacitor may be modeled as two conducting plates separated by a dielectric. When a voltage v is applied across the plates, a charge +q accumulates on one plate and a charge –q on the other.

FORMULAE:

• Total capacitance of a capacitor                                                                                                       
• Charge in a Capacitor                                                                                                                       
  
• Current in a Capacitor                                                                                                                      
  
• Voltage across the capacitor plates                                                                                                   
  
• The electric field generated across the plates                                                                                   
  
• Capacitive reactance                                                                                                                         
  

CAPACITORS IN SERIES

Capacitors get funky when placed in series. The total capacitance of N capacitors in series is the inverse of the sum of all inverse capacitance.

CAPACITORS IN PARALLEL

When capacitors are placed in parallel with one another the total capacitance is simply the sum of all capacitance.

C = C1 + C2

TYPES OF CAPACITORS

1) Ceramic Capacitors
2) Aluminum and tantalum Electrolytic capacitors
3) Super Capacitors
4) Film capacitors
5) Variable capacitors

CAPACITOR APPLICATIONS

1) Decoupling
2) Power Supply Filtering
3) Energy storage and Supply
4) Signal filtering
5) De-Rating

INDUCTOR

An inductor is a passive electronic component that stores energy in the form of a magnetic field. The inductance L represents the efficiency of storing magnetic flux. Unit: henry or H. Symbol: L

MAGNETIC FLUX 

Magnetic flux is a measurement of the total magnetic field which passes through a given area.
Unit: Weber or Wb. Symbol: ϕ

ϕ = B.A