Lecture Notes 1 (Nature of Electricity) - DONE PDF

EE 40 Basic Electrical Engineering I. Nature of Electricity  ELECTRICITY We see applications of electricity all around us, especially in the electronic products we own and operate every day. Electricity itself can be explained in terms of electric charge, voltage, and current. Electr...

EE 40 Basic Electrical Engineering I. Nature of Electricity  ELECTRICITY We see applications of electricity all around us, especially in the electronic products we own and operate every day. Electricity itself can be explained in terms of electric charge, voltage, and current. Electricity is a form of energy, where energy refers to the ability to do work. More specifically, electrical energy refers to the energy associated with electric charges.  ELECTRICITY SIMPLE RECALL OF FUNDAMENTALS OF PHYSICS  ELEMENTARY PARTICLES Electrons – are negatively charged particles. Protons – are positively charged. Neutrons – are electrically neutral (no charge). STABLE PARTICLES IN THE ATOM  STRUCTURE OF MATTER Matter is anything that has mass and occupies space. Matter also is composed of very small particles called atoms. Atoms are composed of subatomic particles of Electrons, Protons, and neutrons. As atoms combine they form either an element or a compound. STABLE PARTICLES IN THE ATOM  STRUCTURE OF MATTER Element – substance consisting of atoms of only one kind. This is considered as the elementary (irreducible) chemical identity of materials. Compound – a combination of two or more different atoms or elements. Most of the insulators are compound. Molecule – the smallest part STABLE PARTICLES INorTHE of a compound ATOM that retains all the material properties of the compound.  STRUCTURE OF MATTER Atomic Number – represents the number of protons in the nucleus of an atom, which in a neutral atom equals the number of electron outside the nucleus. This number determines the place of the element in the periodic table of elements. Atomic Mass – mass of the atom, which represents the sum of protons and STABLE PARTICLES IN THE ATOM neutrons. Electrons has a relatively very small mass and therefore neglected.  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 = 𝟐𝒏𝟐STABLE ; where n is theINnth PARTICLES THEshell ATOM  BOHR ATOMIC MODEL Valence Shell – is the outer most shell or the last shell. This shell or orbit is filled with the remaining electrons. Valence electron(s) - electron(s) that occupies the valence shell or the last shell. Free electrons – are originally valence electrons. As they gain enough energy they escape STABLE from the valence shell and become free. PARTICLES IN THE ATOM It is the movement of free electrons that provides electric current in a metal conductor.  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. It allow electrical current to flow easily because they STABLE have more PARTICLES free IN THE electrons. ATOM Semiconductor – with exactly four valence electrons. It have electrical characteristics in between conductors and insulators. Insulator – material with more than four valence electrons. It will not allow electric current to flow easily because they have very few or even no free electrons.  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 electron volt (eV). Valence band – the region STABLE wherePARTICLES the valence shell IN THE ATOMand 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 at this band have higher energy level than those electrons at the valence band. Forbidden band – the region in an atom where no electron exist. It is in between two allowed bands, such as between valence and conduction bands. ENERGY BANDS STABLE PARTICLES IN THE ATOM  THE COULOMB (UNIT OF CHARGE Q) Is a fundamental property of matter and is influenced by elementary particles such as electrons and protons. According to Benjamin Franklin, there are two kinds of charges, positive charge and negative charge. The unit of electric charge is Coulomb (C), named after Charles Augustin STABLE PARTICLES IN THE ATOM de Coulomb. -1 Coulomb = 6.242 x x 1018 electrons Electron charge = -1.602 x 10−19 Proton charge = 1.602 x 10−19  THE COULOMB (UNIT OF CHARGE Q) Uncharged atom – the number of negatively charged electrons and the number of positively charged protons are equal. Uncharged body – the material whose atoms are uncharged. Charged atom – when an atom loses or gains electron, it becomes electrically unbalanced. Charged body – the material where charged atom belongs. Ion – also known as charges atom and charged STABLE body. PARTICLES IN THE ATOM Cation – atom that losses electron lacks negative charge and the atom becomes positively charged. ion. Electropositive Elements – elements that give up electrons in chemical reactions to produce positive ions. Metallic in nature. Anion – atom that gains electron will have more negative charge and atom becomes negatively charge ion. Electronegative Elements – elements that accept electrons in chemical reactions to produce negative ions. Nonmetallic in nature. ELECTRIC FIELD and ELECTRIC FORCE When the body is electrically charged, it is said to have electric field is 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 STABLE PARTICLES IN THE ATOM particle or body. Electric force – the force produced due to the electric filed of a charged particle or body.  POTENTIAL DIFFERENCE Electrical potential energy – charged bodies tend to move charged particles, it is said to have a capacity to do work or it has potential to do work. Electrical potential – the ability of a charged body to do work on charged particles such as electrons. Electrical potential difference – the difference between the capacities (potentials) of two charges to do work. STABLE PARTICLES IN THE ATOM Volt (V) – the unit of potential difference. A potential of 1 volt has the capacity to do 1 Joule of work in moving 1 Coulomb of charge. Named after Alessandro Volta in 1881. Electromotive Force (emf) – the electrical force that moves charged particles such as electrons.  CURRENT The movement or the flow of electrons is called current. To produce current, the electrons must be moved by a potential difference. Current is represented by the letter symbol I. 𝚫𝑸 𝑪𝒐𝒖𝒍𝒐𝒎𝒃 STABLE PARTICLES IN THE ATOM I= (Ampere) 𝚫𝒕 𝒔𝒆𝒄𝒐𝒏𝒅 One AMPERE of current is defined as the movement of one coulomb past any point of a conductor during one second of time.  CURRENT Example 1: If a current of 2A flows through a meter for 1 minute (min), how many coulombs pass through the meter? STABLE PARTICLES IN THE ATOM Answer: 120C  CURRENT Example 2: The charge of 12 C moves past a given point every second. How much is the intensity of charge flow? STABLE PARTICLES IN THE ATOM Answer: I = 12A  CURRENT Current Density (J) – the current per unit cross-sectional area. I Ampere J= A m2 STABLE PARTICLES IN THE ATOM Direct Current – charges flow in one direction only. Alternating Current – the motion of electric charges is periodically reversed. Conventional Current – the assumption, which considered the flow of charge from positive to negative. This is opposite to the actual charge flow, which is form negative to positive.  MATERIAL RESISTANCE RESISTANCE (R) - is opposition to current. - the ability of a material to oppose or block the flow of charge of current. The resistance of material depends on its dimensions and type. 𝒍 R=ρ 𝑨 The practical unit of resistance is the ohm (Ω) MATERIAL RESISTANCE  MATERIAL RESISTANCE CONDUCTANCE (G) - The opposite of resistance is conductance. The lower the resistance, the higher the conductance. Its symbol is G , and the unit is the Siemens (S).  GENERAL SOURCES OF ELECTRICITY Static Electricity by Friction: electrons in an insulator can be separated by the work of rubbing to produce opposite charges that remain in the dielectric. Examples of how static electricity can be generated include combing your hair Conversion of Chemical Energy: Wet or dry cells and batteries are the applications  GENERAL SOURCES OF ELECTRICITY Electromagnetism: Electricity and magnetism are closely related. Any moving charge has an associated magnetic field; also, any changing magnetic fi eld can produce current. A motor is an example showing how current can react with a magnetic field to produce motion. Photoelectricity: Some materials are photoelectric, that is, they can emit electrons when light strikes the surface. The element cesium is often used as a source of photoelectrons. https://tinyurl.c om/5z6vbcde