LEARNING OUTCOMES At the end of this subject, students should be able to: ➢Understand the basic of electrical concepts. ➢Recognize some common electrical components and measuring instruments. ➢State basic electrical and magnetic quantities and their units. ➢Use scientific notation (power of ten) to express quantities. ➢Use engineering notation and metric prefixes to express large and small quantities. OUTLINE •Basic Electrical concept •Units of Measurement •Scientific Notation •Metric unit Conversions •Atoms •Voltage, current and resistance BASIC CONCEPT • Such interconnection is referred to as an electric circuit, and each component of the circuit is known as an element. • An electric circuit is an interconnection of electrical elements. SYSTEMS OF UNITS • The International System of Units (French: Système international d'unités, SI) is the modern form of the metric system, and is the most widely used system of measurement. • It comprises a coherent system of units of measurement built on seven base units. It defines twenty-two named units, and includes many more unnamed coherent derived units. • The system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. SI Fundamental Units SI Base Units Some Important Electrical Units A single electron has a charge of: 1.602 × 10-19C Charge: The concept of electric charge is the underlying principle for all electrical phenomena. Charge is an electrical property of the atomic particles of which matter consists, measured in coulombs (C). Scientific Notation Definition Scientific notation is simply a method for expressing, and working with very large or very small numbers. It is a short hand method for writing numbers, and an easy method for calculations Like this: Or this: It makes it easy to use big and small values. Metric Prefixes METRIC PREFIX SYMBOL POWER OF TEN femto f 10-15 pico p 10-12 nano n 10-9 micro µ 10-6 mili m 10-3 kilo k 103 mega M 106 giga G 109 tera T 1012 47,000,000 = 4.7 x 107 (Scientific Notation) = 47 x 106 (Engineering Notation) = 47M 0.000 027 = 2.7 x 10-5 (Scientific Notation) = 27 x 10-6 (Engineering Notation) = 27 µ 0.605 = 6.05 x 10-1 (Scientific Notation) = 605 x 10-3 (Engineering Notation) = 605 m When converting from a larger unit to a smaller unit, move the decimal point to the right. Smaller unit 0.47 MW = 470 kW Larger number When converting from a smaller unit to a larger unit, move the decimal point to the left. Remember, a larger unit means the number must be smaller. Larger unit 10,000 pF = 0.01 mF Smaller number When adding or subtracting numbers with a metric prefix, convert them to the same prefix first. 10,000 W + 22 kW = 10,000 W + 22,000 W = 32,000 W Alternatively, 10 kW + 22 kW = 32 kW When adding or subtracting numbers with a metric prefix, convert them to the same prefix first. 200 mA + 1.0 mA = 200 mA + 1,000 mA = 12,000 mA Alternatively, 0.200 mA + 1.0 mA = 1.2 mA THE ATOM Definition: The basic building block Structure: Planetary type of structure -similar to Solar System Consists: Central nucleus surrounded by orbiting electrons Nucleus consists of positively charged particles called protons and uncharged particles called neutrons The negative particles are called electrons 15 THE BOHR MODEL - - ❑ Bohr Model showing the protons, neutrons and electrons in an atom. ❑Protons: basic particles of +ve charge. - - - ❑Electrons: basic particles of -ve charge. always in motion. ❑Neutrons: uncharged particles. ❑Nucleus: the combination of both neutrons and protons. centre of the atom 16 The Valence shell • The outer shell is called the valence shell. Electrons in this shell are involved in chemical reactions and they account for electrical and thermal conductivity in metals. + Shell 1 Shell 2 Shell 3 Electrical charges • Opposite electrical charges always attract each other. • So these particles with opposite charges will tend to move toward each other. • Like electrical charges always repel. So particles with like charges will move away from each other. • Remember: Opposites charges attract, and like charges repel. • Atoms always try to remain electrically balanced. + + _ + Ion Particles When an atom loses or gains an electron, an imbalance occurs. The atom becomes either a positively or negatively charged particle called an ION. These unbalanced charged ION particles are responsible for electron flow (electricity). IONs will take or release an electron to become balanced again. Electron Orbits • Electrons rotate around the atom at different orbits called Rings, Orbits or Shells. • BOUND ELECTRONS orbit the nucleus on the inner rings. Bound electrons have a strong magnetic attraction to the nucleus. • FREE ELECTRONS orbit on the outermost ring which is known as the VALANCE RING. Voltage • Force is required to move a charge against the electric field. • When force is applied over a distance, work is done. Work done in moving a charge against the electric field leads to the definition of voltage: • Voltage is the work per charge done against the electric field. • The defining equation for voltage is W V= Q Where: V = voltage in volts (V) W = energy in joules (J) Q = charge in coulombs (C) Measurement • A VOLTMETER measures the voltage potential across or parallel to the circuit. • The Voltmeter measures the amount of electrical pressure difference between two points being measured. • Voltage can exist between two points without electron flow. Voltage units • Voltage is measured in units called VOLTS. • Voltage measurements can use different value prefixes such as millivolt, volt, Kilovolt, and Megavolt. Current (Amperes) • • CURRENT is the quantity or flow rate of electrons moving past a point within one second. Current flow is also known as amperage, or amps for short. Higher voltage will produce higher current flow, and lower voltage will produce lower current flow. I = 𝑄 𝑡 Where: I = current in amperes (A) Q = charge in coulombs (C) t = time in seconds (s) Current • Current Flow theories ❑Two Current Flow theories exist. The first is: • Electron Theory ❑ The Electron Theory states that current flows from NEGATIVE to POSITIVE. Electrons move from atom to atom as they move through the conductor towards positive. • Current Flow theories ❖The second Current Flow theory is: • Conventional Theory ❖ Conventional theory, also known as HOLE THEORY, states that current flows from POSITIVE to NEGATIVE. Protons or the lack of electrons (the holes) move towards the negative. (Current flow direction in Hole Theory is the opposite of that in Electron Theory.) Measurement • • An AMMETER measures the quantity of current flow. Ammeters are placed in series (inline) to count the electrons passing through it. Example: A water meter counts the gallons of water flowing through it. Amperage Units • Current flow is measured in units called Amperes or AMPS. • Amperage measurements can use different value prefixes, such as microamp, milliamp, and Amp. Resistance • Resistance is the force that reduces or stops the flow of electron. It opposes voltage. • Higher resistance will decrease the flow of electrons and lower resistance will allow more electrons to flow. Measurement • An OHMMETER measures the resistance of an electrical circuit or component. No voltage can be applied while the ohmmeter is connected, or damage to the meter will occur. • Example: Water flows through a garden hose, and someone steps on the hose. The greater the pressure placed on the hose, the greater the hose restriction and the less water flows. Resistance Units • Resistance is measured in units called OHMS. • Resistance measurements can use different value prefixes, such as Kilo ohm and Megaohms. Components designed to have a specific amount of resistance are called resistors. Color bands Resistance material (carbon composition) Insulation coating Leads Resistance Color Code Resistance value, first three bands: First band – 1st digit Second band – 2nd digit *Third band – Multiplier (number of zeros following second digit) Fourth band - tolerance For resistance values less than 10 W, the third band is either gold or silver. Gold is for a multiplier of 0.1 and silver is for a multiplier of 0.01. What is the resistance and tolerance of each of the four-band resistors? 5.1 kW ± 5% 820 kW ± 5% 47 W ± 10% 1.0 W ± 5% Resistors (4- Band) 1st Band (Kuning) 2nd Band (Ungu) Formula: 3rd Band (Kuning) AB x 10c +/- D% = 47 x 104 +/- 10% th 4 Band (Perak) Hitam Coklat Merah Oren Kuning Hijau Biru Ungu Kelabu Putih Emas Perak Tiada War (0) (1) (2) (3) (4) (5) (6) (7) (8) (9) (5%) (10%) (20%) Haji Cik Mat Orang Kaya Hendak Beli Ubi Kayu Putih Enggan Pulang Tanpa Wang POWER • Electric power is the rate at which electric energy is transferred. Electric power is measured by capacity and is commonly expressed in megawatts (MW). A megawatt (MW) is one million watts. • The electrical energy supplied by a current to an appliance enables it to do work or provide some other form of energy such as light or heat. • When a direct current of I Amperes is flowing in an electric circuit and the voltage across the circuit is V volts, then the power in watts is P = IV • Sign of power •• Plus sign: Power is absorbed by the element. (resistor, inductor) • Minus sign: Power is supplied by the element. (battery, generator) • Passive sign convention: • If the current enters through the positive polarity of the voltage, p = vi. • If the current enters through the negative polarity of the voltage, p = -vi. • The total power supplied to the circuit must balance the total power absorbed. EXAMPLES Types Of Electricity • Two basic types • • of Electricity classifications: Static Electricity is electricity that is standing still. Voltage potential with NO electron flow. Dynamic Electricity is electricity that is in motion. Voltage potential WITH electron flow. Two types of Dynamic electricity exist: • Direct Current (DC) Electron Flow is in only one direction. • Alternating Current (AC) Electron flow alternates and flows in both directions (back and forth).
