Circuits 1 – Module 2A

1. Circuits 1 – Module 2A ELEL31E Prepared by: Engr. Ronaldo Amos

2. Circuits 1 – Module 2A • Definition of Electricity • SI System of Measurement • Electric charge • Structure of matter • Electrical classification of materials • Electric field and electric force • Electric potential • Electric current, direction of flow • Material resistance

3. Fundamentals of Electricity Electricity • Is an electric charge, or an electrical energy or electromagnetic energy • Static electricity • Moving electric current • Phenomenon associated with the presence and motion of electrons and other charged particles • The physical phenomena arising from the behavior of electrons and protons that is caused by the attraction of particles with opposite charges and the repulsion of particles with the same charge. • The flow of electrons and protons in a closed circuit due to electric charge. • When a potential difference between two charges forces a third charge to move, the charge in motion is called and electric current. • The flow of electric current in a closed circuit

4. SI system of measurement • SI stands for International System of Units • At present, two major systems—the English (US Customary) and the metric—are in everyday use. • Examples of metric: meter, kg, ampere, joule, hertz, ohm • Examples of English: inch, pound, ft, horsepower, ft-lb • The SI system combines the MKS metric units and the electrical units into one unified system • Though the use of SI system is very wide, there are instances where expressing it in English system is more practical. For example, the HP as a unit of power is preferred over W when it comes to very large quantities. Thus, it is necessary to know the conversion of these units from SI to English and vise-versa. • Unit Conversion • Example: convert 12 cm to inches • 12cm x 1in/2.54cm = 4.72 in

7. Unit Prefixes • Kilo = K = 103 • Mega = M = 106 • Giga = G = 109 • Tera = T = 1012 • Milli = m = 10-3 • Micro = µ = 10-6 • Nano = n = 10-9 • Pico = p = 10-12 • Usually resistances are expressed in , K , M , and G . • Amperes are usually expressed in A, mA, and µA. • Voltages in electronics are usually expressed in V, mV, and µV. In electrical, voltages may go up to several KV, and MV.

8. Conversion of Unit

9. Sample Problem:

10. Electric charge (Q) • Is a fundamental property of matter and is influenced by elementary particles such as electrons and protons • A body is said to be charged, if it has an excess or deficit of electrons from its normal values due to sharing. • The quantity of electron flow or charge • 2 kinds of charges according to Benjamin Franklin (US scientist: 1706 – 1790) • Positive charge (carried by protons) • Negative change (carried by electrons) • Unit: Coulomb Symbol: C • Named after the French physicist, Charles Augustin de Coulomb (1736 – 1806) • 1 coulomb = 6.242 x 1018 electrons • Electron charge = 1/6.242 x 1018 = 1.602 x 10-19 C • Like poles repel, unlike poles attract. Like charges repel, unlike charges attract.

11. Structure of Matter • The elementary particles are basic form of matter, • and as they combine they form another matter, • the atom; and as atoms combine forms yet another different matter • Matter – is anything in the universe that has mass, occupies space, and is convertible to energy. • Compound – a combination of two or more different atoms or elements. • Element – substance consisting of atoms of only one kind. This is considered as the elementary (irreducible) chemical identity of materials which means that it cannot be decomposed any further by chemical action. • Molecule – the smallest particle that a compound can be reduced before it breaks down into its elements. It’s the smallest part of a compound or material that retains all the properties of the compound. • Atom – smallest part of that an element can be reduced to and still keeping the properties of the element. • Atomic number – represents the number of protons in the nucleus of an atom, which in a neutral atom equals the number of electrons outside the nucleus. • Atomic mass – mass of the atom, which represents the sum of protons and neutrons. Electrons has a relatively very small mass and therefore neglected. • Valence electrons – electrons found in the outermost shell or orbit of an atom

12. Bohr Atomic Model • Electric current – the directional motion of electrons • Electrostatics – deals with stationary charged particles • Magnetism – effects of moving electrons • Electromagnetism – magnetism due to electric current. Electron charge = -1.602 x 10-19 C Proton charge = +1.602 x 10-19 C Neutron = 0 C Joseph John Thomson (1856 – 1940) A British physicist who discovered the electron in 1897, which he initially called corpuscles, meaning a living cell.

13. Bohr Atomic Model • Niels Henrik David Bohr (1885 – 1962) • Danish physicist who in 1913 developed a new model of atomic structure call the Bohr Atomic Model. • In this model, electrons travel in defined circular orbits around the nucleus. The orbits are labeled by an integer, the quantum number n. • Electrons can jump from one orbit to another by emitting or absorbing energy. • The maximum number of electrons (Ne) that can occupy a given shell or the nth shell can be approximated by: • Ne = 2n2where n is the nth shell • Example: Cu 29 electrons • 1st shell, n=1; Ne = 2 electrons • 2nd shell, n=2 ; Ne = 8 electrons • 3rd shell, n= 3; Ne = 18 electrons • 4th shell, Ne = 1 valence electron = 29 – 28 • Note: the farther the electron from the nucleus, the higher is its energy level

14. Mass of • Electron = 9.109 x 10-13 kg • Proton = 1.673 x 10-27 kg • Neutron = 1.673 x 10-27 kg • Charge to mass ratio (C/kg) • Electron = 1.76 x 1011 • Proton = 3.58 x 107 • Valence shell – is the outer most shell or the last shell. • Free electrons – are originally valence electrons. As they gain enough energy they escape from the valence shell and become free • Free electrons do not remain permanently associated with the atoms of a solid, they move from one atom to another and during conduction of electricity, it is these free electrons that will be in motion.

15. Coulomb’s Law • The force between charges was studied by the French scientist Charles Coulomb (1736–1806). • Coulomb determined experimentally that the force between two charges Q1 and Q2 (Figure 2–5) is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. • where Q1 and Q2 are the charges in coulombs, • r is the center-to-center spacing between them in meters, and • k = 9 x 109.

16. Electrical Classifications of Material: • the number of valence electrons is a common indication that tells us the electrical characteristics of a material. • Conductor – material with less than four valence electrons. Conductors allow electrical current to flow easily because they have more free electrons. • Insulator – material with more than four valence electrons. Insulators will not allow electrical current to flow easily because they have few or even no free electrons. • Semiconductor – with exactly four valence electrons. Semiconductors have electrical characteristics in between conductors and insulators.

17. Energy bands • Before a valence electron can escape from its shell and becomes free, it must gain energy of at least equal to the energy gap • Energy gap – the energy difference between the valence band and conduction band. Its unit is the electron volt (eV) • 1eV = 1.6 x 10-19 Joule • A unit of energy equal to the energy gained by an electron in passing from a point of low potential to a point one volt higher in potential. • Valence band – the region where the valence shell and valence electrons are occupying. It is the highest energy level before conduction band. • Conduction band – the region where free electrons are said to be present . Electrons a this band have a higher energy level than those electrons at the valence band. • Forbidden band – the region in an atom where no electrons exist. It is in between two allowed bands, such as between valence and conduction bands.

18. Energy Band Diagram of an Atom Highest energy level Conduction band Energy gap (Eg) Forbidden Band Valence shell level Valence band Levels bet.1st energy level & valence band Increasing energy level 1st energy level Forbidden Band 1st shell closest to the nucleus electrons Nucleus Ground State Energy gap (Eg) of : Conductors = 0 eV Insulators > 5 eV Semiconductors = 1eV Eg = 0 means that the valence electrons can easily become free. This explains why conductors have the most number of free electrons and can easily support electric current flow.

19. Law of Conservation of Charge: • The net charge of an isolated system remains constant. The only way to change the net charge of a system is to bring in charge from elsewhere, or remove charge from the system. • Law of Conservation of Charge-Energy: • Electric charge is neither created nor destroyed but is transferred from one body to another. • Ion – a charged body • Anion – negatively charged ion • Cation – positively charged ion • Electropositive elements are elements that give up electrons in chemical reactions to produce positive ions. These elements are metallic in nature. • Electronegative elements are elements that accept electrons in chemical reactions to produce negative ions. These elements are nonmetallic in nature.

20. Electric Field and Electric Force • When the body is electrically charged, it is said to have electric field in its surroundings. This field interacts with other charged bodies and will produce an electric force that may cause them to move. • Electric field – is the area or region surrounding an electrically charged particle or body • Electric force – the force produced due to the electric field of a charged particle or body. • Electric potential • the ability of a charged body to do work on charged particles such as electrons • Electric potential difference – the difference between the capacities (potentials) of two charges to do work. • Volt (V) – the unit of potential difference. A potential of one volt (1V) has the capacity to do one joule (1J) of work in moving one coulomb (1C) of charge. Named after the Italian physicist, Alessandro Volta (1745-1827) • V = W/Q where: w = work or energy in joules Q = charge in coulombs • Voltage – another name for potential difference. • Electromotive force (emf) – the electrical force that moves the charged p;articles such as electrons (electron moving force). The term emf is used interchangeably with potential difference and voltage.

21. Electric current • Any directional movement of electric charges such as electrons. • Current in gases and liquids – generally consist of flow of positive ions in one direction together with a flow o f negative ions in the opposite direction. • Current in solids – such as wires, consist of the flow of electrons, and is a measure of the quantity of charge passing any point of the wire per unit of time. • I = dQ/ dt C/s or Ampere, the intensity of electron flow • Ampere (A) – the unit of electric current. Named in honor to the French physicist and mathematician, Andre M. Ampere (1775 – 1836) • Current density (J) – the current per unit cross-sectional area • J = I/A = ampere/m2 • Closed Circuit – a path for current flow • Open circuit – a path for current flow is cut or opened. • Short circuit – a path for current flow that bypasses a component or sub-circuit, which may create an overload. • Schematic diagram – a diagram that uses symbols for components to draw the circuits • Pictorial diagram – a diagram using pictures of component to show the circuits. • Direct current – charges flow in one direction only • Alternating current – the motion of electric charges is periodically reversed. • Conventional current flow – the flow of charge from positive to negative. • Electron flow – the flow of charge from negative to positive.

22. A guide to solving problems • Determine what is given in the problem, that is, the given scenario or situation. The schematic diagram is usually given for you to draw and identify the known and the unknown in the diagram. • Determine what is being asked by the problem, that is, identify the problem • Determine the theories, principles, formulas related to the problem and the given scenarios or situation • From the formulas that relates the known and the unknown, substitute the given values. • Write your solutions at the point of view of the reader, which means that it must be on a step-by-step process avoiding short cuts that may lead to misunderstanding by the reader. • Write legibly, logically, and highlight your final answer. • Example: • Given: • Find ? • Formula • Solution • Answer inside a box • In your computations, the resolution or number of decimal places of your computed numbers should be at least 2 decimal places more than the highest resolution number in the given data when not exact. • The final answer should have 1 decimal place more than the highest resolution number in the given data when not exact.

23. Sample Problems: • A positively charged dielectric has a charge of 2 coulombs. If 12.5 x 1018 free electrons are added to it, what will be the net charge on the said dielectric? Q1= +2C Q2= -12.5 * 1018e * (1C/6.25 * 1018e) = -2C Qnet= Q1+Q2 = 2 + (-2) Qnet= 0 • A battery can deliver 10 joules of energy to move 5 coulombs of charge. What is the potential difference between the terminals of the battery? Note: volt = joules per coulomb E = W/Q = 10/5 E = 2 volts • A cloud of 2.5 x 1019 electrons move past a given point every 2 seconds. How much is the intensity of the electron flow? Note: ampere = coulombs per second Q = (2.5 * 1019) * 1C/(6.25 * 1018) = 4C I = Q/t = 4/2 I = 2 amperes

24. Sample Problems • The current in an electric lamp is 5 amperes. What quantity of electricity flows towards the filament in 6 minutes? Q = It = 5(6min * (60sec/1min)) Q = 1800 C • A consistent current of 4 A charges a capacitor. How long will it take to accumulate a total charge of 9 coulombs on the plates? t = Q/I = 8/4 t = 2 sec

25. Exercises: • Perform the following conversions: • 27 minutes to seconds • 0.8 hours to seconds • 2 h 3 min 47 s to s • 35 horsepower to watts • 1827 W to hp • 23 revolutions to degrees • Convert the following: • 156 mV to volts • 0.15 mV to microvolts • 47 kW to watts • 0.057 MW to kilowatts • 3.5104 volts to kilovolts • 0.0000357 amps to microamps

26. 3 4. Positive charges Q1 2 mC and Q2 12 mC are separated center to center by 10 mm. Compute the force between them. Is it attractive or repulsive? 5. Two equal charges are separated by 1 cm. If the force of repulsion between them is 9.7 102 N, what is their charge? What may the charges be, both positive, both negative, or one positive and one negative? 6. After 10.61 1013 electrons are added to a metal plate, it has a negative charge of 3 mC. What was its initial charge in coulombs?

27. Homework 3 4 5 6

28. Homework 7 8 9 10 11

29. Special Assignment • Research & Report Different Sources of Electricity (deadline - next week) • Report on AC sources • Report on DC sources • Content: • Source of Electricity – Description • How it generates electricity? • Equipment/ parts/ composition involve, etc. • Energy conversion to electrical energy – process • Control of electricity • Transmission and Distribution • Safety, Length of Life, etc. • Research & Report about Superconductors (deadline – next week)