FUNDAMENTALS OF ELECTRIC CIRCUITS EE 201 Dr. ARVIND TIWARI B1-S DEPARTMENT OF ELECTRICAL ENGINEERING, COLLEGE OF ENGINEERING AL-QASSIM UNIVERSITY 1

Fundamental units : Temperature, Time, Length, Mass, Luminous intensity, Amount of substance, Electric current UNITS OF MEASUREMENT  Derived Units : Area, Volume, Velocity, Acceleration, Kelvin(K), Second(s), Meter(m), Kilogram(Kg), Candela(cd),Mole(mol),Ampere(A) m 2, m 3, ms -1, ms -2 SYSTEMS OF UNITS: MKS, CGS, SI

3 Named units derived from SI base units QuantitySymbolRelationship Dimension symbol AreaAWidth x lenghtm2m2 VolumeVWidth x length x heightm3m3 Velocityu,vDisplacement/timem/s or ms -1 Accelerat e aVelocity/timem/s 2 or ms -2 ForceFMass x accelerationKgms -2 or N PressurepForce / AreaPascal WorkWForce x distanceJoule or Nm PowerPWork/timeJ/s or Watt

4 PREFIXES

CIRCUIT ELEMENTS RESISTOR CURRENT VOLTAGE POWER ENERGY OHM’S Law FUNDAMENTALS OF ELECTRIC CIRCUITS 5

Circuit Elements 5 ideal basic circuit elements: –voltage source –current source –resistor –inductor –Capacitor Many practical systems can be modeled with just sources and resistors The basic analytical techniques for solving circuits with inductors and capacitors are the same as those for resistive circuits active elements, capable of generating electric energy passive elements, incapable of generating electric energy 6

ATOMS AND THEIR STRUCTURE The orbiting electron carries a negative charge equal in magnitude to the positive charge of the proton In all other elements, the nucleus also contains neutrons, which are slightly heavier than protons and have no electrical charge. 7

The atomic structure of any stable atom has an equal number of electrons and protons. The number of electrons in each succeeding shell is determined by 2n 2 where n is the shell number. 8

VOLTAGE Every source of voltage is established by simply creating a separation of positive and negative charges COULOMB’S LAW 9 One coulomb of charge is the total charge associated with 6.242X10 18 electrons

Q. Find the voltage between two points if 60 J of energy are required to move a charge of 20 C between the two points. if a total of 1 joule (J) of energy is used to move the negative charge of 1 coulomb (C), there is a difference of 1 volt (V) between the two points. VOLTAGE 10

CURRENT The applied voltage is the starting mechanism—the current is a reaction to the applied voltage AT ROOM TEMPERATURE: net flow in any one direction is zero. BY APPLYING A VOLTAGE 11

The current in amperes is given by The applied voltage (or potential difference) in an electrical/electronics system is the “pressure” to set the system in motion, and the current is the reaction to that pressure. if 6.242x10 18 electrons (1 coulomb) pass through the imaginary plane in 1 second, the flow of charge, or current, is 1 ampere (A). 12

13 VOLTAGE SOURCES An electromotive force (emf) is a force that establishes the flow of charge (or current) in a system due to the application of a difference in potential. DC voltage sources can be divided into three basic types: (1)batteries (chemical action or solar energy), (2)generators (electromechanical), (3)power supplies

CONDUCTORS, SEMICONDUCTORS AND INSULATORS Conductors are those materials that permit a generous flow of electrons with very little external force (voltage) applied. Good conductors typically have only one electron in the valence (most distant from the nucleus) ring. Insulators are those materials that have very few free electrons and require a large applied potential (voltage) to establish a measurable current level. Semiconductors are a specific group of elements that exhibit characteristics between those of insulators and those of conductors. Semiconductor materials typically have four electrons in the outermost valence ring. 14

The opposition to the flow of charge through an electrical circuit, called resistance, has the units of ohms ( Ω ). RESISTANCE: CIRCULAR WIRES The resistance of any material is due primarily to four factors: 1. Material 2. Length 3. Cross-sectional area 4. Temperature of the material The material is identified by a factor called the resistivity, which uses the Greek letter rho (r). 15 RESISTANCE

The higher the resistivity, the greater the resistance of a conductor. The longer the conductor, the greater the resistance The greater the area of a conductor, the less the resistance 16

METRIC UNITS 17

18 TEMPERATURE EFFECTS Conductors An increase in temperature results in an increase in the resistance level. Consequently, conductors have a positive temperature coefficient. Semiconductors An increase in temperature results in a decrease in the resistance level. Consequently, semiconductors have negative temperature coefficients.

Insulators An increase in temperature results in a decrease in the resistance of an insulator. The result is a negative temperature coefficient. 19

20 Temperature Coefficient of Resistance The higher the temperature coefficient of resistance for a material, the more sensitive the resistance level to changes in temperature.

TYPES OF RESISTORS Fixed Resistors

Variable Resistors 22

CONDUCTANCE The reciprocal of the resistance of a material, measure of how well the material conducts electricity. The quantity is called conductance, G, siemens (S) 23

24 OHM’S LAW The symbol E is applied to all sources of voltage The symbol V is applied to all voltage drops across components of the network

For any resistor, in any network, the direction of current through a resistor will define the polarity of the voltage drop across the resistor 25

26 1.Determine the current resulting from the application of a 9 V battery across a network with a resistance of 2.2 Ω. 2. Calculate the resistance of a 60 W bulb if a current of 500 mA results from an applied voltage of 120 V.

POWER It provides an indication of how much work (energy conversion) can be accomplished in a specified amount of time; that is, power is a rate of doing work. The power associated with any supply is not simply a function of the supply voltage. It is determined by the product of the supply voltage and its maximum current rating. 27

ENERGY The energy (W) lost or gained by any system is determined by Since power is measured in watts (or joules per second) and time in seconds, the unit of energy is the watt- second or joule 28