Electricity-Part 1 Lesson in Physics for Engineers
- 1. Electricity – PART 1 PHYSICS FOR ENGINEERS PREPARED BY: ENGR. REY S.A. RIMANDO, CE RMP LPT INSTRUCTOR
- 2. The Origin of Electricity The electrical nature of matter is inherent in atomic structure.
- 3. ATOMIC STRUCTURE • An atom is visualized as having a planetary type of structure that consists of a central nucleus surrounded by orbiting electrons. o Electron was discovered by Joseph John Thomson in 1897 o Proton was discovered by Ernest Rutherford in 1918 o Neutron was discovered by James Chadwick in 1932 • It is the smallest particle of an element. • There are 118 known elements that have atoms and are different from the atoms of other elements. ATOM BOHR’S MODEL
- 6. ATOMIC NUMBER • It is a number that represents the arrangement of all elements in the periodic table. • It is equal to the number of protons or electrons in an electrically balanced atom.
- 7. SHELL, ORBIT, AND ENERGY LEVEL ● Electrons orbit the nucleus of an atom at specific level from the nucleus. Orbit is a discrete distance from the nucleus corresponds to a certain energy level that are grouped into energy bands called shells which is designated as K, L, M and so on. Each shell can have a fix maximum number of electrons given by the equation: Where: n = energy level, such as 1,2, 3, and so on • The further the distance of the orbit, the higher the energy level. The lowest energy level is also called GROUND STATE. • Electrons, as they acquire enough energy, can jump from one energy level to a higher one. • Electrons near the nucleus are the weakest and those in the outermost orbit are the strongest. Maximum Electrons in each Shell = 𝟐𝐧𝟐
- 8. VALENCE ELECTRON • There is a force of attraction between the positively charged nucleus and the negatively charged electron. And this force decreases with an increasing distance between the particles. It means that the electrons orbiting in the outermost shell have higher energy and are less tightly bounded to the atom. • Outermost shell is sometimes called Valence shell and the electrons orbiting this shell are called valence electrons. • Valence Electron is important for some chemical bonding within the structure and electrical properties of a certain material.
- 9. IONIZATION • When the atom absorbs energy, such as heat, valence electrons may acquire enough energy that can let them escape from its shell and the atom’s influence. This process of losing valence electrons is called ionization that may result to a positively charge atom called positive ion or cation. • Elements that gives up electrons during chemical reaction to produce cation are called ELECTROPOSITIVE ELEMENTS. • Escaped valence electrons are called FREE ELECTRONS, that when loses energy may fall to a neutral atom resulting to a negatively charged particle called negative ion or anion. • Elements that receive electrons during chemical reaction to produce anion are called ELECTRONEGATIVE ELEMENTS.
- 10. In nature, atoms are normally found with equal numbers of protons and electrons, so they are electrically neutral. By adding or removing electrons from matter it will acquire a net electric charge with magnitude equal to e times the number of electrons added or removed, N. Electric Charge
- 11. Example 1 How many electrons are there in one coulomb of negative charge?
- 12. Electric Charge
- 18. Coulomb’s Law States that “The force of attraction or repulsion between two electrically charged bodies is proportional to the magnitude of their charges and inversely proportional to the square of the distance separating them.” Mathematically, 𝑭 = 𝒌 𝒒𝟏 𝒒𝟐 𝒓𝟐 𝑘 = 1 4𝜋𝜀0 ≈ 9 × 109 𝑁 𝑚2 /𝐶2 Where: ε0 = permittivity of free space = 8.854 × 10−12 F/m r = distance between 𝐪𝟏 𝐚𝐧𝐝 𝐪𝟐
- 20. Electric Field
- 22. Example The charges on the two metal spheres and the ebonite rod create an electric field at the spot indicated. The field has a magnitude of 2.0 N/C. Determine the force on the charges in (a) and (b)
- 24. Example The isolated point charge of q=+0.8μC is in a vacuum. The test charge is 0.20m to the right and has a charge qo=+15μC. Determine the electric field at point P.
- 26. Work Done in Moving a Charge in an Electric Field
- 27. CAPACITORS
- 28. Capacitors Basic Concepts ● A capacitor is a passive electrical component that stores electrical charge and has a property of capacitance. ● It is constructed of two parallel conductive plates separated by an insulating material called the dielectric. ● It has a property called capacitance, ability to store charge, expressed in Farad (F).
- 29. Capacitors Storing charges ● Uncharged capacitor has an equal number of free electrons for both plates. ● When a voltage source is connected to the capacitor leads, through a resistor, capacitor begins to charge. The plates will gain and lose electrons until the voltage in the capacitor equals the voltage source. ● If the capacitor is disconnected from the source, it retains the stored charge for a long period of time (the length of time depends on the type of capacitor) and still has the voltage across it. ● A charged capacitor can act as a temporary battery.
- 30. Capacitance ● It is the amount of charge that a capacitor can store per unit of voltage across its plates, designed as C. ● It is the measure of a capacitor’s ability to store charge. 𝐂 = 𝐐 𝐕 Where: C = capacitance (F) Q = charge (C) V = voltage (V)
- 31. STORING ENERGY ● A capacitor stores energy in the form of an electric field that is established by the opposite charges stored on the two plates. ● The electric field is represented by lines of force between the positive and negative charges and is concentrated within the dielectric. Coulomb’s law states: ● A force (F) that exist between two point-source charges (q1 and q2) is directly proportional to the product of two charges and inversely proportional to the square of the distance (r) between charges. ● Opposite charges distributed on the plates of a capacitor create lines of force, which form an electric field that stores energy within the dielectric. Capacitors 𝑭 = 𝒌 𝒒𝟏 𝒒𝟐 𝒓𝟐
- 32. Capacitors ● The greater the force between the charges on the plates of a capacitor, the more energy is stored. 𝑾 = 𝟏 𝟐 𝑪𝑽𝟐 Where: W = energy (J) C = capacitance (F) V = voltage (V)
- 33. Capacitors PHYSICAL CONCEPT ● The following parameters are important in establishing the capacitance and the voltage rating of a capacitor: plate area, plate separation, and dielectric constant. 𝐂 = 𝐀𝛆 𝐝 𝜺𝒓 = 𝛆 𝜺𝟎 Where: C = capacitance (F) A = plate area (𝑚2) d = distance between the plate (m) 𝛆 = absolute permittivity of the material (m) 𝜺𝒓= relative permittivity (dielectric constant), unitless 𝜺𝟎= absolute permittivity of free space/ vacuum = 8.854 × 10−12 𝐹 𝑚
- 34. Material Relative Permittivity (𝜺𝒓) Air (Vacuum) 1.0 Teflon 2.0 Paper (paraffined) 2.5 Oil 4.0 Mica 5.0 Glass 7.5 Ceramic 1200
- 35. Capacitors Dielectric Materials ● It is a substance placed in between the plates. ● The most efficient dielectric is air, has almost no loss but less capacitance. ● Dielectric can increase the capacitance. ● They are considered good insulator. TYPES OF CAPACITOR: ● Fixed or variable ● Polarized or Non-polarized o Depends on the type of dielectric material o Common dielectric materials: mica, ceramic, plastic-film, and electrolytic (aluminum oxide and tantalum oxide).
- 36. Capacitors labeling ● Typographical labeling o Uses letters and numbers o Indicates capacitance, voltage rating, and tolerance.
- 37. Capacitor color coding ● The color code used for capacitors is basically the same as that used for resistors. Some variations occur in tolerance designation.
- 38. Series Capacitors 𝑄𝑇 = 𝑄1 = 𝑄2 = 𝑄3 … 𝑉𝑇 = 𝑉1 + 𝑉2 + 𝑉3 … 𝐶𝑇 = 1 1 𝐶1 + 1 𝐶2 + 1 𝐶3 … For two capacitors in series: 𝐶𝑇 = 𝐶1𝐶2 𝐶1 + 𝐶2
- 39. Parallel Capacitors 𝑄𝑇 = 𝑄1 + 𝑄2 + 𝑄3 … 𝑉𝑇 = 𝑉1 = 𝑉2 = 𝑉3 … 𝐶𝑇 = 𝐶1+ 𝐶2+ 𝐶3 …
- 40. Example: Capacitances of 3μF, 6μFand 12μFare connected in series across a 350V supply. Calculate (a) the equivalent circuit capacitance, (b) the charge on each capacitor and (c) the voltage across each capacitor.
- 42. Example: For the arrangement shown in figure find (a) the equivalent capacitance of the circuit, (b) the voltage across QR and (c) the charge on each capacitor.
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