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Basic Electrical and Electronics Notes
Typology: Lecture notes
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SCE Page 1 of 226 DEPARTMENT OF
A Course Material on
GE 6252 BASIC ELECTRICAL AND ELECTRONICS ENGINEERING
By
Mrs. R.HEMALATHA
Mrs.K.UMARANI
Mr.S.VIJAY
Mr.R.GUNASEKARAN
ASSISTANT PROFESSOR
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
SASURIE COLLEGE OF ENGINEERING
VIJAYAMANGALAM – 638 056
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This is to certify that the e-course material
Subject Code : GE 6252
Subject: Basic Electrical and Electronics Engineering
Class : I Year Mechanical
Being prepared by me and it meets the knowledge requirement of the university curriculum.
Signature of the Author
Name:
Designation:
This is to certify that the course material being prepared by Mrs. Hemalatha.R is of adequate
quality. She has referred more than five books among them minimum one is from abroad author.
Signature of HD
Name:
SEAL
Construction, Principle of Operation of Single phase induction Motor
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4.5 Flip- Flops 140
4.6 Registers and Counters 146
4.7 A/D and D/A Conversion 150
5.1 Types of Signals Analog and Digital Signals 156
5.2 Modulation and Demodulation Principles of Amplitude. 158
Modulation and Demodulation Principles of Frequency Modulations.
5.4 Block diagram of Radio 164
5.5 Block diagram of TV 170
5.6 Block diagram of Microwave 173
5.7 Block diagram of Satellite 175
5.8 Block diagram of Optical Fiber 176
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Prerequisites
Solid, Liquid and gas particles called molecules. These molecules are made up of atoms which can be further spilt into electrons, protons and neutrons. The electrons revolve around the nucleus. The electrons presents in the outer most orbits experience a very weak force of attraction for the obvious reason that according to coulomb’s law, the force between two charges varies inversely with the square of the distance. These electrons are known as free electrons. The movement of electrons are known as electric current
Introduction 1.1 Basic Definitions Electric current: The continuous flow of electrons constitutes electric current. It is denoted by ‘I’ and is measured in amperes.
‘I’ is also given by I = coulomb / sec
Electric Potential: The electric potential at any point in an electric field is defined as the work done in brining an unit positive charge (Q) from infinity to that point against the electric field
‘V’ is given by V =
Resistance: It is the property of a conductor by which it opposes the flow of current. It is denoted by R and its unit is ohms (Ω)
Laws of resistance: The resistance of a conductor (i). Varies directly with its length (l) (ii).Varies inversely with its cross sectional area (A) (iii). Depends on the nature of the material (iv). Depends on the temperature R α L And R α 1/A R α L / A R = ρ L / A Where ρ is called specific resistance
Specific resistance: It is defined as the resistance offered by unit cube of the material between its opposite faces. It is denoted by ρ and its unit is ohm – meter ρ = RA / L
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Temperature effect on resistance: In the case of pure metals the resistance increases with increases in temperature. In case of alloys the increase in resistance with increases in temperature is relatively small and irregular. The resistance of electrolytes and insulators decreases with increases in temperature
Temperature co-efficient of resistance It is defined as the change in resistance per ohm per degree change in temperature from 0°C. If a material has resistance of R 0 , R 1 , and R 2 at temperature of 0°C, t 1 °C and t 2 °C respectively, then
R 1 = R 0 (1 + α 0 t 1 ) R 2 = R 0 (1+ α 0 t 2 )
R 2 = R 1 (1+α 0 (t 2 -t 1 ))
αt =
1.2. DC Circuits: Prerequisites: A DC circuit (Direct Current circuit) is an electrical circuit that consists of any combination of constant voltage sources, constant current sources, and resistors. In this case, the circuit voltages and currents are constant, i.e., independent of time. More technically, a DC circuit has no memory. That is, a particular circuit voltage or current does not depend on the past value of any circuit voltage or current. This implies that the system of equations that represent a DC circuit do not involve integrals or derivatives.
Introduction: In electronics, it is common to refer to a circuit that is powered by a DC voltage source such as a battery or the output of a DC power supply as a DC circuit even though what is meant is that the circuit is DC powered.
If a capacitor and/or inductor is added to a DC circuit, the resulting circuit is not,
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conductor and the conductor become a magnet. This phenomenon is called electromagnetism. Since the magnet is produced electric current, it is called the electromagnet. An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current. The magnetic field disappears when the current ceases. In short, when current flow through a conductor, magnetic field will be generated. When the current ceases, the magnetic field disappear.
Applications of Electromagnetism: Electromagnetism has numerous applications in today's world of science and physics. The very basic application of electromagnetism is in the use of motors. The motor has a switch that continuously switches the polarity of the outside of motor. An electromagnet does the same thing. We can change the direction by simply reversing the current. The inside of the motor has an electromagnet, but the current is controlled in such a way that the outside magnet repels it.
Another very useful application of electromagnetism is the "CAT scan machine." This machine is usually used in hospitals to diagnose a disease. As we know that current is present in our body and the stronger the current, the strong is the magnetic field. This scanning technology is able to pick up the magnetic fields, and it can be easily identified where there is a great amount of electrical activity inside the body
The work of the human brain is based on electromagnetism. Electrical impulses cause the operations inside the brain and it has some magnetic field. When two magnetic fields cross each other inside the brain, interference occurs which is not healthy for the brain.
Ohm’s Law: Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them. The mathematical equation that describes this relationship is:
where I is the current through the resistance in units of amperes, V is the potential difference measured across the resistance in units of volts, and R is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent of the current.
AC Circuits: Prerequisites: An alternating current (AC) is an electrical current, where the magnitude of the
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current varies in a cyclical form, as opposed to direct current, where the polarity of the current stays constant.
The usual waveform of an AC circuit is generally that of a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves
Introduction:
Used generically, AC refers to the form in which electricity is delivered to businesses and residences. However, audio and radio signals carried on electrical wire are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal.
Kirchhoff’s law: Kirchhoff's Current Law: First law (Current law or Point law): Statement: The sum of the currents flowing towards any junction in an electric circuit equal to the sum of currents flowing away from the junction.
Kirchhoff's Current law can be stated in words as the sum of all currents flowing into a node is zero. Or conversely, the sum of all currents leaving a node must be zero. As the image below demonstrates, the sum of currents Ib, Ic, and Id, must equal the total current in Ia. Current flows through wires much like water flows through pipes. If you have a definite amount of water entering a closed pipe system, the amount of water that enters the system must equal the amount of water that exists the system. The number of branching pipes does not change the net volume of water (or current in our case) in the system.
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Steady State Solution of DC Circuits: Resistance in series connection:
The resistors R 1 , R 2 , R 3 are connected in series across the supply voltage “V”. The total current flowing through the circuit is denoted as “I”. The voltage across the resistor R 1 , R 2 and R 3 is V 1 , V 2 , and V 3 respectively. V 1 = IR 1 (as per ohms law) V 2 = IR 2 V 3 = I*R 3 V = V 1 +V 2 +V 3 = IR 1 +IR 2 +IR 3 = (R 1 +R 2 +R 3 ) I IR = (R 1 +R 2 +R 3 ) I R = R 1 +R 2 +R 3
Resistance in parallel connection:
The resistors R 1 , R 2 , R 3 are connected in parallel across the supply voltage “V”. The total current flowing through the circuit is denoted as “I”. The current flowing through the resistor R 1 , R 2 and R 3 is I 1 , I 2 , and I 3 respectively.
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I = V / R (as per ohms law)
I 1 = V 1 / R 1 I 2 = V 2 / R 2 I 3 = V 3 / R 3 V 1 = V 2 = V 3 = V From the above diagram I = I 1 +I 2 +I 3 = V 1 / R 1 + V 2 / R 2 + V 3 / R 3 = V / R 1 + V/R 2 +V/R 3 I = V (1/R 1 +1/R 2 +1/R 3 ) V / R = V (1/R 1 +1/R 2 +1/R 3 ) 1/R = 1/R 1 +1/R 2 +1/R 3
Problems based on ohm’s law
Problem 1: A current of 0.5 A is flowing through the resistance of 10Ω.Find the potential difference between its ends.
Given data: Current I= 0.5A.
Resistance R=1Ω
T o f i n d
Potential difference V =?
Formula used:
V = IR
Solution: V = 0.5 × 10 = 5V.
Result :
The potential difference between its ends = 5 V
Problem : A supply voltage of 220V is applied to a 100 Ω resistor. Find the current flowing through it. Given data
Voltage V = 220V Resistance R = 100Ω
To find:
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Solution: Current I = P / V = 100 / 200 = 0.5 A Resistance R = V / I = 200 / 0. = 400 Ω
Result: The value of the current I = 0.5 A The value of the Resistance R = 400 Ω
Problem: 5 A circuit is made of 0.4 Ω wire, a 150Ω bulb and a 120Ω rheostat connected in series. Determine the total resistance of the circuit. Given data: Resistance of the wire = 0.4Ω Resistance of bulb = 1 5 0 Ω Resistance of rheostat = 120Ω To find: The total resistance of the circuit R (^) T =? Formula used: The total resistance of the circuit R (^) T = R 1 +R 2 +R 3 Solution: Total resistance ,R = 0.4 + 150 +
= 270.4Ω
Result:
The total resistance of the circuit R (^) T = 270.4 Ω
Problem 6:
Three resistances of values 2Ω, 3Ω and 5Ω are connected in series across 20 V, D.C supply .Calculate (a) equivalent resistance of the circuit (b) the total current of the circuit (c) the voltage drop across each resistor and (d) the power dissipated in each resistor.
Given data: R 1 = 2Ω R 2 = 3Ω R 3 = 5Ω V = 20V
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To find: R (^) T =? I (^) T =? V 1 , V 2 , V 3 =? P 1 , P 2 , P 3 =?
Formula used: RT = R 1 +R 2 +R 3 (series connection) IT = VT / RT V 1 = R 1 *I 1 V 2 = R 2 *I 2 V 3 = R 3 *I 3 P 1 =V 1 *I 1 P 2 =V 2 *I 2 P 3 =V 3 *I 3
Solution: RT = R 1 +R 2 +R 3 = 2+3+ RT = 10Ω
IT = VT / RT = 20 / 10 IT = 2 A
In series connection I 1 = I 2 = I 3 = IT = 2A
V 1 = I 1 R 1 = 2 V 1 = 4 V
V 2 = I 2 R 2 = 2 V 2 = 6 V
V 3 = I 3 R 3 = 5 V 3 = 10V
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Resistors are “passive” devices that are they do not produce or consume any electrical energy, but convert electrical energy into heat. In DC circuits the linear ratio of voltage to current in a resistor is called its resistance. However, in AC circuits this ratio of voltage to current depends upon the frequency and phase difference or phase angle ( φ ) of the supply. So when using resistors in AC circuits the term Impedance , symbol Z is the generally used and we can say that DC resistance = AC impedance, R = Z.
It is important to note, that when used in AC circuits, a resistor will always have the same resistive value no matter what the supply frequency from DC to very high frequencies, unlike capacitor and inductors.
For resistors in AC circuits the direction of the current flowing through them has no effect on the behaviour of the resistor so will rise and fall as the voltage rises and falls. The current and voltage reach maximum, fall through zero and reach minimum at exactly the same time. i.e, they rise and fall simultaneously and are said to be “in-phase” as shown below.
We can see that at any point along the horizontal axis that the instantaneous voltage and current are in-phase because the current and the voltage reach their maximum values at the same time, that is their phase angle θ is 0 o. Then these instantaneous values of voltage and current can be compared to give the ohmic value of the resistance simply by using ohms law. Consider below the circuit consisting of an AC source and a resistor.
The instantaneous voltage across the resistor, VR is equal to the supply voltage, Vt and is given as: VR = Vmax sinωt
The instantaneous current flowing in the resistor will therefore be: IR = VR / R = Vmax sinωt / R = I (^) max sinωt
In purely resistive series AC circuits, all the voltage drops across the resistors can be added together to find the total circuit voltage as all the voltages are in-phase with each other. Likewise,
in a purely resistive parallel AC circuit, all the individual branch currents can be added together
to find the total circuit current because all the branch currents are in-phase with each other.
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Since for resistors in AC circuits the phase angle φ between the voltage and the current is zero, then the power factor of the circuit is given as cos 0 o^ = 1.0. The power in the circuit at any instant in time can be found by multiplying the voltage and current at that instant.
Then the power (P), consumed by the circuit is given as P = Vrms Ι cos Φ in watt’s. But since cos Φ = 1 in a purely resistive circuit, the power consumed is simply given as, P = Vrms Ι the same as for Ohm’s Law.
This then gives us the “Power” waveform and which is shown below as a series of positive pulses because when the voltage and current are both in their positive half of the cycle the resultant power is positive. When the voltage and current are both negative, the product of the two negative values gives a positive power pulse.
Then the power dissipated in a purely resistive load fed from an AC rms supply is the same as that for a resistor connected to a DC supply and is given as: P = V rms * I rms = I 2 rms * R = V 2 rms / R
Pure Inductive circuits:
This simple circuit above consists of a pure inductance of L Henries ( H ), connected across a sinusoidal voltage given by the expression: V(t) = Vmax sin ωt. When the switch is closed this sinusoidal voltage will cause a current to flow and rise from zero to its maximum value. This rise
