Basic Electrical Concepts | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) PDF Download

Some of the Basic Concepts include :

1. Electric Current

The rate of flow of electric charge through any point of the circuit is called electric current. Its unit is ampere, denoted by A.

2. Coulomb's Law

According to this law, the force of attraction or repulsion between stationary point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

Where K = 9 X    

N

3. Electric Field

It is the region surrounding an electric charge or group of charges, in which another charge experiences a force of attraction or repulsion.

4. Electric Lines of Forces

• An electric lines of force field along which a free isolated unit positive charge moves.
• Electric lines of force start from the positive charge and end to the negative charge.
• No two lines of force can intersect each other because if they do so, then at the point of intersection two tangents can be drawn which would mean two directions of force at that point which is impossible.
• These lines have a tendency to separate from each other in the direction perpendicular to their length.
• Lines of force of uniform field are parallel.
• Lines of force leaves the surface of the conductor normally.

5. Electric Flux

The total number of the electric field lines passing a given area in the unit of time is known as the electric flux.

When the plane is irregular at an angle θ, then the projected area is Acosθ, and the total flux through this surface is given as-

Where,

E = Magnitude of the electric field.

A = Area of the surface through which the electric flux is calculated.

θ = The angle made by the axis and the plane that is parallel to the direction of flow of an electric field.

Unit of Electric Flux

• V . m
• Nm m²C⁻¹
• Base unit: Kg. m³s⁻³A⁻¹

6. Ohm's Law

According to this law if there is no charge the physical state of conductor (Such as temp.) then the current flowing through the conductor is directly proportional to the voltage applied i, e.

I α V .

I =

• V is the potential difference measured across the conductor (in volts)
  I  is the current through the conductor (in amperes)
  R is the constant of proportionality called resistance (in ohms)
• A graph between applied voltage and current is a straight line shows that it follows ohm's law.
• Ohm's law is valid for metallic conductors only.

7. Resistance

It is a measure of opposition to the flow of electric current.

Electrical resistance is directly proportional to length (L) of the conductor and inversely proportional to the cross-sectional area (A). It is given by the following relation.

Note:The reciprocal of resistivity is called conductivity.

  (Ohm – m)–1 = mho/meter.

Colour Code for Resistances:

• Resistor colour codes, introduced by the Radio Manufacturers Association (RMA) in the 1920s, are used to represent resistance values, tolerance, and sometimes reliability on tiny resistors, typically up to one watt. These codes consist of 3 to 6 colour bands, with the first two indicating resistance value, the third as a multiplier, and additional bands specifying tolerance or reliability. This system simplifies reading resistance values without requiring printed numbers.
• These resistances are usually carbon resistances and whose code is used to indicate the value of resistance. 
• A carbon resistance has usually 4 concentric rings or bands A, B, C, D of different colours.
  
• The colour of first two bands A and B indicate the 1st two significant figures of resistance in ohms & those of 3rd band C indicate the decimal multiplies. The 4th band D (Which is either silver or gold) tells the tolerance. 
• Sometimes only 3 colour band is there (A, B and C).

NOTE: B B ROY Great Britain Very Good Wife.   

Resistor colour table

8. Electric Potential

The electric potential at a point in an electric field is the ratio of the work done in bringing a test charge from infinity to that point to the magnitude of the test change. 

If the work done in moving a test charge q₀ from infinity to that point against the field is W, then

9. Potential Gradient

The potential gradient is the rate of change of electric potential with respect to distance in an electric field. It is mathematically expressed as:

10. Electric Potential Energy

The electric potential energy of a system of charges is the work that has to be done in bringing these charges from infinity to near each other to form the system.

The potential energy of a system of charges q₁ and q₂ separated by a distance 'r' is

11. Capacitor

An element in which energy is stored in the form of an electrostatic field is called a capacitor.

•  It functions similarly to a rechargeable battery. 
• Capacitors come in various types, including small beads used in resonance circuits and larger ones for power factor correction. 
• Despite their differences, all capacitors serve the same purpose of energy storage.
•  Essentially, a capacitor consists of two or more conductive plates that are not connected or in contact with each other.

Practical Capacitor

Capacitor Circuit diagram

12. Capacitance

• Capacitance refers to a capacitor's ability to store electrical energy and is measured in farads, a unit named after the British physicist Michael Faraday.
•  It is defined as the ability of a capacitor to store one coulomb of charge to create a 1-volt potential difference. 
•  Since the farad is a large unit, capacitance is often measured in smaller units such as pico-farads, nano-farads, and micro-farads.
• 
• The physical features of a capacitor determine the value of its capacitance – the area of the capacitor, the distance between the plates of the capacitor, and the dielectric medium’s permittivity, ∈₀ = 8.85 x 10^-12 
• Unit – C²N^–1 M^–2

Energy stored in a capacitor:

Energy(E) =  

=  

= C.  

13. Inductor

An inductor is a component that does not require power to operate and is commonly used in various power electronic circuits. 

• Its main function is to store energy as magnetic energy when electricity flows through it. 
• The unit of measurement for inductance is the Henry. 
•  The key characteristic of an inductor is its inductance, which is defined as the ratio of the voltage across it to the rate at which the current changes. This inductance arises from the magnetic field created around the coil of wire. 
• Several factors influence the level of inductance, including: 
  • The shape of the coil.
  • The number of turns and layers of wire in the coil.
  • The spacing between the turns of wire.
  • The permeability of the core material used.
  • The size of the core itself.

One henry is defined as the inductance of a coil in which a change in current of one ampere per second induces a voltage of one volt.

Formula:The inductance $LL$L of an inductor is given by the formula:

$L=\frac{N}{\mathrm{<sup\; style="word-break:\; break-word;\; line-height:\; 1.8;\; font-family:\; Lato,\; sans-serif;\; font-size:\; 13px\; !important;\; letter-spacing:\; inherit;\; color:\; black">2</sup>}}L\; =\; \backslash frac\{\{N^2\; \backslash mu\; A\}\}\{\{l\}\}$

Where:

• L = Inductance (in henries, H)
• N = Number of turns in the coil
• μ = Permeability of the core material (in henries per meter, H/m)
• A = Cross-sectional area of the coil (in square meters, m²)
• $l$l = Length of the coil (in meters, m)

For a simple circuit, the induced voltage $V$V is related to the rate of change of current $\frac{\mathrm{<img\; src="https://cn.edurev.in/ApplicationImages/Temp/24733558\_5ac30f82-c831-4b7b-83d1-e239cabea215\_lg.png"\; style="display:\; block;\; margin:\; 5px\; auto;\; text-align:\; center;"\; fr-original-class="fr-draggable"\; alt="Basic\; Electrical\; Concepts\; |\; Electrical\; Engineering\; SSC\; JE\; (Technical)\; -\; Electrical\; Engineering\; (EE)">}}{}\backslash frac\{di\}\{dt\}$ by:

$V\; =\; L\; \backslash cdot\; \backslash frac\{di\}\{dt\}$Where:

• $V$V = Induced voltage (in volts, V)
• $L$L = Inductance (in henries, H)
• $\frac{d}{i}\backslash frac\{di\}\{dt\}$= Rate of change of current (in amperes per second, A/s)

Energy stored in Inductor:

= L.  

14. Inductance

Inductance results from the fact that a flow of current produces a magnetic field, according to magnetic field along tends to induce a voltage (or current) in a wire according to Faraday's law.

(i) For RL Load :

V=V_m sin wt

show I lags by 90º R-L Load phasor :-

(ii) For RC Load:

Shows I leads by 90º

(iii) For RC phases:

(iv) For RLC Load:

Case 1: |V_L| >  |V_c|

Case 2: |V_L| <  |V_c|

Case 3: |V_L| =  |V_c|

V = V_R

Ø = 0

CosØ = 1(UPF)

Note:- Reactive power is consumed by energy storing demands.