Fundamentals of Electrical and Electronics

Here Students Understand the All about the Course Structure

What is the Current?

Current is the rate at which electrons flow past a point in a complete electrical circuit. At its most basic,

Current = Flow.

An ampere, or amp, is the international unit used for measuring current. It expresses the quantity of electrons (sometimes called "electrical charge") flowing past a point in a circuit over a given time.

A current of 1 ampere means that 1 coulomb of electrons—that's 6.24 billion billion (6.24 x 1018) electrons—is moving past a single point in a circuit in 1 second.

The calculation is similar to measuring water flow: how many gallons pass a single point in a pipe in 1 minute (gallons per minute, or GPM).

Symbols used for amps:

A = amperes, for a large amount of current (1.000).
mA = milliamperes, a thousandth of an amp (0.001).
µA = microamperes, a millionth of an amp (0.000001).

In formulas such as Ohm's Law, current is also represented by I (for intensity).

Amps are named for French mathematician/physicist Andrè-Marie Ampére (1775-1836), credited for proving:

• A magnetic field is generated around a conductor as current passes through it.

• The strength of that field is directly proportional to the amount of current flowing.

Electrons flow through a conductor (typically a metal wire, usually copper) when two prerequisites of an electric circuit are met:

1. The circuit includes an energy source (a battery, for instance) that produces voltage. Without voltage, electrons move randomly and fairly evenly within a wire, and current cannot flow. Voltage creates pressure that drives electrons in a single direction.

2. The circuit forms a closed, conducting loop through which electrons can flow, providing energy to any device (a load) connected to the circuit. A circuit is closed (complete) when a switch is turned to the ON, or closed, position (see diagram at the top of this page).

Current, like voltage, can be direct or alternating.

Direct current (dc):

• Represented by the symbols or on a digital multimeter.

• Flows only in one direction.

• Common source: batteries or dc generator.

Alternating current (ac):

• Represented by the symbols or on a digital multimeter.

• Flows in a sine wave pattern (shown below); reverses direction at regular intervals.

• Common source: household electrical receptacles powered by a public utility.

What is voltage?

Voltage is the pressure from an electrical circuit's power source that pushes charged electrons (current) through a conducting loop, enabling them to do work such as illuminating a light.

In brief, voltage = pressure, and it is measured in volts (V). The term recognizes Italian physicist Alessandro Volta (1745-1827), inventor of the voltaic pile—the forerunner of today's household battery.

In electricity's early days, voltage was known as electromotive force (emf). This is why in equations such as Ohm's Law, voltage is represented by the symbol E.

Example of voltage in a simple direct current (dc) circuit:

1. In this dc circuit, the switch is closed (turned ON).

2. Voltage in the power source—the "potential difference" between the battery's two poles—is activated, creating pressure that forces electrons to flow as current out the battery's negative terminal.

3. Current reaches the light, causing it to glow.

4. Current returns to the power source.

Voltage is either alternating current (ac) voltage or direct current (dc) voltage. Ways they differ:

Alternating current voltage (represented on a digital multimeter by ):

• Flows in evenly undulating since waves, as shown below:

• Reverses direction at regular intervals.

• Commonly produced by utilities via generators, where mechanical energy—rotating motion powered by flowing water, steam, wind or heat—is converted to electrical energy.

• More common than dc voltage. Utilities deliver ac voltage to homes and businesses where the majority of devices use ac voltage.

• Primary voltage supplies vary by nation. In the United States, for example, it's 120 volts.

• Some household devices, such as TVs and computers, utilize dc voltage power. They use rectifiers (such as that chunky block in a laptop computer's cord) to convert ac voltage and current to dc.

Direct current voltage (represented on a digital multimeter by and ):

• Travels in a straight line, and in one direction only.

• Commonly produced by sources of stored energy such as batteries.

• Sources of dc voltage have positive and negative terminals. Terminals establish polarity in a circuit, and polarity can be used to determine if a circuit is dc or ac.

• Commonly used in battery-powered portable equipment (autos, flashlights, cameras).

What is Energy?

Energy is essential to life and all living organisms. The sun, directly or indirectly, is the source of all the energy available on Earth. In Physics, energy is a quantitative property that must be transferred to an object in order for it to perform work. Hence we can define energy as the strength to do any kind of physical activity. Thus, they say,

Energy is the ability to do work

Energy is a conserved quantity and the law of conservation of energy states that energy can neither be created nor destroyed but can only be converted from one form to another. The SI unit of energy is Joule.

Units of Energy

The international system of units of measurement of energy is Joule. The unit of energy is named after James Prescott Joule. Joule is a derived unit and it is equal to the energy expended in applying a force of one newton through a distance of one metre. However, energy is also expressed in many other units not part of the SI, such as ergs, calories, British Thermal Units, kilowatt-hours and kilocalories, which require a conversion factor when expressed in SI units.

What is Power?

We can define power as the rate of doing work, it is the work done in unit time. The SI unit of power is Watt (W) which is joules per second (J/s). Sometimes the power of motor vehicles and other machines are given in terms of Horsepower (hp), which is approximately equal to 745.7 watts.

What is Average Power?

We can define average power as the total energy consumed divided by the total time taken. In simple language, we can say that average power is the average amount of work done or energy converted per unit of time.

Power Formula

Power is defined as the rate at which work is done upon an object. Power is a time-based quantity. which is related to how fast a job is done. The formula for power is mentioned below.

Power = Work / time

P = W / t

Unit of Power

The unit for standard metric work is the Joule and the standard metric unit for time is the second, so the standard metric unit for power is a Joule / second, defined as a Watt and abbreviated W.

QUIZ of module 1

What is the Resistor?

The resistor is a passive electrical component to create resistance in the flow of electric current. In almost all electrical networks and electronic circuits they can be found. The resistance is measured in ohms. An ohm is the resistance that occurs when a current of one ampere passes through a resistor with a one volt drop across its terminals. The current is proportional to the voltage across the terminal ends. This ratio is represented by Ohm’s law:

R= V / I

Resistors are used for many purposes. A few examples include delimit electric current, voltage division, heat generation, matching and loading circuits, control gain, and fix time constants. They are commercially available with resistance values over a range of more than nine orders of magnitude. They can be used to as electric brakes to dissipate kinetic energy from trains, or be smaller than a square millimeter for electronics.

Resistor definition and symbol

A resistor is a passive electrical component with the primary function to limit the flow of electric current. The international IEC symbol is a rectangular shape. In the USA the ANSI standard is very common, this is a zigzag line.

Resistors can be divided in construction type as well as resistance material. The following breakdown for the type can be made:

• Fixed resistors

• Variable resistors, such as the:

• Potentiometer

• Rheostat

• Trimpot

Resistance dependent on a physical quantity:

• Thermistors (NTC and PTC) as a result of temperature change

• Photo resistor (LDR) as a result of a changing light level

• Varistor (VDR) as a result of a changing voltage

• Magneto resistor (MDR) as a result of a changing magnetic field

• Strain Gauges as a result of mechanical load

Resistor applications

There is a huge variation in fields of applications for resistors; from precision components in digital electronics, till measurement devices for physical quantities. In this chapter several popular applications are listed.

Resistors in series and parallel

In electronic circuits, resistors are very often connected in series or in parallel. A circuit designer might for example combine several resistors with standard values (E-series) to reach a specific resistance value. For series connection, the current through each resistor is the same and the equivalent resistance is equal to the sum of the individual resistors. For parallel connection, the voltage through each resistor is the same, and the inverse of the equivalent resistance is equal to the sum of the inverse values for all parallel resistors. In the articles resistors in parallel and series a detailed description of calculation examples is given. To solve even more complex networks, Kirchhoff’s circuit laws may be used.

What is capacitor?

Capacitor is an electronic component that stores electric charge. The capacitor is made of 2 close conductors (usually plates) that are separated by a dielectric material. The plates accumulate electric charge when connected to power source. One plate accumulates positive charge and the other plate accumulates negative charge.

The capacitance is the amount of electric charge that is stored in the capacitor at voltage of 1 Volt.

The capacitance is measured in units of Farad (F).

The capacitor disconnects current in direct current (DC) circuits and short circuit in alternating current (AC) circuits.

Capacitance

The capacitance (C) of the capacitor is equal to the electric charge (Q) divided by the voltage (V):

Capacitance of plates capacitor

The capacitance (C) of the plates capacitor is equal to the permittivity (ε) times the plate area (A) divided by the gap or distance between the plates (d):

Capacitors in series

The total capacitance of capacitors in series, C1,C2, C3,.. :

Capacitors in parallel

The total capacitance of capacitors in parallel, C1,C2,C3,.. :

CTotal = C1+C2+C3+...

Capacitor's current

The capacitor's momentary current ic(t) is equal to the capacitance of the capacitor,

times the derivative of the momentary capacitor's voltage vc(t):

Capacitor's voltage

The capacitor's momentary voltage vc(t) is equal to the initial voltage of the capacitor,

plus 1/C times the integral of the momentary capacitor's current ic(t) over time t:

Energy of capacitor

The capacitor's stored energy EC in joules (J) is equal to the capacitance C in farad (F) times the square capacitor's voltage VC in volts (V) divided by 2:

EC = C × VC 2 / 2

AC circuits

Angular frequency

ω = 2π f

ω - angular velocity measured in radians per second (rad/s)

f - frequency measured in hertz (Hz).

Capacitor's reactance

What is an Inductor?

The inductor is perhaps the simplest of all electronic components, constructed much like a resistor – a simple length of wire that is coiled up. However, here, resistance is not the property we’re looking for. It is something that happens because of the shape of the wire – a coil – it creates a magnetic field when a current is passed through it. This induced magnetic field gives this bit of wire some interesting electrical properties, especially inductance – which gives these parts their name.

Difference between an Inductor and Capacitor

We have already learnt about the capacitor in the previous article. And now that you have known the basics of inductor you might get a question, “What is the difference between an Inductor and Capacitor?”

First things first both store energy when a voltage potential is applied across it, but a Capacitor stores energy in form of an Electric Field and an Inductor stores energy in form of a Magnetic felid. Okay, but how does it affect its performance.

We need a dig a lot deep in to understand that, but for now you can just remember that a Capacitor tries to level the voltage in a circuit, that is it does not like the change in potential across each component and hence it will charge or discharge to level up the voltage. An Inductor on the other hand does not like the change in current within a circuit so it the current changes it will charge or discharge to equalize the current through the circuit.

Also remember that an Inductor changes it polarity while discharging so the potential during charging will be opposite to the potential during dis-charge.

Symbols for Inductors

Like many other electronic components, the symbol for an inductor is a simplified pictogram of what it actually looks like:

Measuring an Inductor

The working behavior of an inductor poses an interesting question – how do we quantitatively measure the behavior of an inductor in terms that is easily measurable?

We could try measuring inductors by the magnetic field that they create. As soon as we do that, we run into problems. The magnetic field created by an inductor depends on the current that passes through it, so even a small inductor can create a large magnetic field.

Instead, we could use the same approach we used for capacitors, and we can define inductance of a circuit as the voltage change induced when the current changes at a certain rate.

Mathematically,

V = L(dI/dt)

Where V is the voltage, L is the inductance, I is the current and t is the time period.

Inductance, ‘L’, is measured in Henrys, named after Joseph Henry, the American scientist who discovered electromagnetic induction.

The formula for calculating the inductance of a coil of wire is given by this formula:

L =(µn2a)/l

Where L is the inductance in Henrys, µ is the permeability constant, i.e. a coefficient of how easily the magnetic field can be created in a given medium, n is the number of turns, a is the area of the coil and l is the length of the coil.

Again, the Henry is a very large unit, so practically inductors are measured in microHenrys, uH, which is a millionth of a Henry, or milliHenrys, mH, which is a thousandth of a Henry. Occasionally you might even find very small inductances measured in nanoHenrys, which are a thousandth of a uH.

QUIZ for Module 2

What is a diode?

A diode is a semiconductor device that essentially acts as a one-way switch for current. It allows current to flow easily in one direction, but severely restricts current from flowing in the opposite direction.

Diodes are also known as rectifiers because they change alternating current (ac) into pulsating direct current (dc). Diodes are rated according to their type, voltage, and current capacity.

Diodes have polarity, determined by an anode (positive lead) and cathode (negative lead). Most diodes allow current to flow only when positive voltage is applied to the anode. A variety of diode configurations are displayed in this graphic

Diodes are available in various configurations. From left: metal case, stud mount, plastic case with band, plastic case with chamfer, glass case.

When a diode allows current flow, it is forward-biased. When a diode is reverse-biased, it acts as an insulator and does not permit current to flow.

What is Transistor?

Definition: The transistor is a semiconductor device which transfers a weak signal from low resistance circuit to high resistance circuit. The words trans mean transfer property and istor mean resistance property offered to the junctions. In other words, it is a switching device which regulates and amplify the electrical signal likes voltage or current.

The transistor consists two PN diode connected back to back. It has three terminals namely emitter, base and collector. The base is the middle section which is made up of thin layers. The right part of the diode is called emitter diode and the left part is called collector-base diode. These names are given as per the common terminal of the transistor. The emitter based junction of the transistor is connected to forward biased and the collector-base junction is connected in reverse bias which offers a high resistance.

Transistor Terminals

The transistor has three terminals namely, emitter, collector and base. The terminals of the diode are explained below in details.

Emitter – The section that supplies the large section of majority charge carrier is called emitter. The emitter is alway connected in forward biased with respect to the base so that it supplies the majority charge carrier to the base. The emitter-base junction injects a large amount of majority charge carrier into the base because it is heavily doped and moderate in size.

Collector – The section which collects the major portion of the majority charge carrier supplied by the emitter is called a collector. The collector-base junction is always in reverse bias. Its main function is to remove the majority charges from its junction with the base. The collector section of the transistor is moderately doped, but larger in size so that it can collect most of the charge carrier supplied by the emitter.

Base – The middle section of the transistor is known as the base. The base forms two circuits, the input circuit with the emitter and the output circuit with the collector. The emitter-base circuit is in forward biased and offered the low resistance to the circuit. The collector-base junction is in reverse bias and offers the higher resistance to the circuit. The base of the transistor is lightly doped and very thin due to which it offers the majority charge carrier to the base.

Working of Transistor

Usually, silicon is used for making the transistor because of their high voltage rating, greater current and less temperature sensitivity. The emitter-base section kept in forward biased constitutes the base current which flows through the base region. The magnitude of the base current is very small. The base current causes the electrons to move into the collector region or create a hole in the base region.

The base of the transistor is very thin and lightly doped because of which it has less number of electrons as compared to the emitter. The few electrons of the emitter are combined with the hole of the base region and the remaining electrons are moved towards the collector region and constitute the collector current. Thus we can say that the large collector current is obtained by varying the base region.

Transistor Operating Conditions

When the emitter junction is in forward biased and the collector junction is in reverse bias, then it is said to be in the active region. The transistor has two junctions which can be biased in different ways. The different working conduction of the transistor is shown in the table below.

FR – In this case, the emitter-base junction is connected in forward biased and the collector-base junction is connected in reverse biased. The transistor is in the active region and the collector current is depend on the emitter current. The transistor, which operates in this region is used for amplification.

FF – In this condition, both the junction is in forward biased. The transistor is in saturation and the collector current becomes independent of the base current. The transistors act like a closed switch.

RR – Both the current are in reverse biased. The emitter does not supply the majority charge carrier to the base and carriers current are not collected by the collector. Thus the transistors act like a closed switch.

RF – The emitter-base junction is in reverse bias and the collector-base junction is kept in forward biased. As the collector is lightly doped as compared to the emitter junction it does not supply the majority charge carrier to the base. Hence poor transistor action is achieved.

QUIZ for Module 3

What is Ohm’s Law?

Ohm's Law is a formula used to calculate the relationship between voltage, current and resistance in an electrical circuit.

To students of electronics, Ohm's Law (E = IR) is as fundamentally important as Einstein's Relativity equation (E = mc²) is to physicists.

E = I x R

When spelled out, it means voltage = current x resistance, or volts = amps x ohms, or V = A x Ω.

Named for German physicist Georg Ohm (1789-1854), Ohm's Law addresses the key quantities at work in circuits

What is the Kirchhoff Circuit Law?

We saw in the Resistors tutorial that a single equivalent resistance, ( RT ) can be found when two or more resistors are connected together in either series, parallel or combinations of both, and that these circuits obey Ohm’s Law.

However, sometimes in complex circuits such as bridge or T networks, we can not simply use Ohm’s Law alone to find the voltages or currents circulating within the circuit. For these types of calculations we need certain rules which allow us to obtain the circuit equations and for this we can use Kirchhoffs Circuit Law.

In 1845, a German physicist, Gustav Kirchhoff developed a pair or set of rules or laws which deal with the conservation of current and energy within electrical circuits. These two rules are commonly known as: Kirchhoffs Circuit Laws with one of Kirchhoffs laws dealing with the current flowing around a closed circuit, Kirchhoffs Current Law, (KCL) while the other law deals with the voltage sources present in a closed circuit, Kirchhoffs Voltage Law, (KVL).

Kirchhoffs First Law – The Current Law, (KCL)

Kirchhoffs Current Law or KCL, states that the “total current or charge entering a junction or node is exactly equal to the charge leaving the node as it has no other place to go except to leave, as no charge is lost within the node“. In other words the algebraic sum of ALL the currents entering and leaving a node must be equal to zero, I(exiting) + I(entering) = 0. This idea by Kirchhoff is commonly known as the Conservation of Charge.

Kirchhoffs Current Law

Here, the three currents entering the node, I1, I2, I3 are all positive in value and the two currents leaving the node, I4 and I5 are negative in value. Then this means we can also rewrite the equation as;

I1 + I2 + I3 – I4 – I5 = 0

The term Node in an electrical circuit generally refers to a connection or junction of two or more current carrying paths or elements such as cables and components. Also for current to flow either in or out of a node a closed circuit path must exist. We can use Kirchhoff’s current law when analysing parallel circuits.

Kirchhoffs Second Law – The Voltage Law, (KVL)

Kirchhoffs Voltage Law or KVL, states that “in any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop” which is also equal to zero. In other words the algebraic sum of all voltages within the loop must be equal to zero. This idea by Kirchhoff is known as the Conservation of Energy.

Kirchhoffs Voltage Law

Starting at any point in the loop continue in the same direction noting the direction of all the voltage drops, either positive or negative, and returning back to the same starting point. It is important to maintain the same direction either clockwise or anti-clockwise or the final voltage sum will not be equal to zero. We can use Kirchhoff’s voltage law when analysing series circuits.

When analysing either DC circuits or AC circuits using Kirchhoffs Circuit Laws a number of definitions and terminologies are used to describe the parts of the circuit being analysed such as: node, paths, branches, loops and meshes. These terms are used frequently in circuit analysis so it is important to understand them.

Common DC Circuit Theory Terms:

· Circuit – a circuit is a closed loop conducting path in which an electrical current flows.

· Path – a single line of connecting elements or sources.

· Node – a node is a junction, connection or terminal within a circuit were two or more circuit elements are connected or joined together giving a connection point between two or more branches. A node is indicated by a dot.

· Branch – a branch is a single or group of components such as resistors or a source which are connected between two nodes.

· Loop – a loop is a simple closed path in a circuit in which no circuit element or node is encountered more than once.

· Mesh – a mesh is a single closed loop series path that does not contain any other paths. There are no loops inside a mesh.

QUIZ for Module 4