1.1 Basic Electrical Quantities Quantities Definition Symbol Unit Electromotive force (emf) Force /electric pressure that cause the flow of electrons, or The flow of current in circuit E Volt (V) Charge Types of charge : positive and negative charge Q Coulomb (C) Current Movement of electric charge cause by free electrons movement Flows from positive to negative terminal I Ampere (A) Potential energy (voltage) Potential different between 2 points in an electric circuit V Volt (V) Resistance Property of material which oppose the flow of current through it R Ohm (Ω) Resistivity Electrical property of a material that quantifies how strongly a given material opposes the flow of electric current ρ Ohm meter (Ωm) Factors Affect Resistance No. Factors Description i. Length of material The longer the length of the wire, the higher the resistance value ii. Resistivity The higher the resistance, higher the resistivity iii. Area The resistance increase, the cross section area of a conductor will decreases iv. Temperature The conductor temperature increase, the value of resistance also increase Where: Quantities Symbol Unit Cross sectional area A = Meter square (m2 ) Resistivity ρ = Ohm meter (Ωm) Length l = Meter (m) Resistance R = Ohm (Ω) R L R ρ R A R T Chapter 1 : Introduction to Electrical Circuits ~ An energy which cannot see, but can be felt ~ Electric energy can be created from impact from action as friction, heat and electromagnetic field ~ Electric energy can change into : Light energy – lamp Heat energy – iron Sound energy – radio Kinetic energy - motor ~ 2 types of electric Static electricity – no electron movement Dynamic electricity – Got electron movement
1.2 Types of Electrical Circuits No. Electric Circuits Description Types of Electric Circuits Description Figure i. Complete electric circuit (close circuit) Circuit forms complete loop The current go through completely from source and back flow to source again Must have V, I and R Simple circuits / Basic circuit A simple circuit may include two components : a battery and a lamp ii. Complex Circuit Combination of components such as resistors, capacitors, transistor etc. iii. Non complete electric circuit The current flow will never happen without one of 3 components : V / I / R Open circuits No current flow occur Loose connection / damaged component iv. Short circuits Circuit without load The connection at load, will short with conductor Use of Voltmeter, Ammeter and Ohm Meter Factors Use Unit Voltmeter Measure electrical potential difference between two points in an electric circuit Voltage (V) Ammeter Measure the electric current in a circuit Ampere (A) Ohm meter Measure electric resistance in a circuit Ohms (Ω) Wattmeter Measure value of electric power (or the supply rate of electric energy) Watt (W) Multimeter Measure two or more electrical values
1.3 Ohm’s Law Definition At constant temperature, the electric current (I) flowing in conducting material is directly proportional to the applied voltage (V) and inversely proportional to the resistance (R) (Pada suhu malar, arus elektrik (I) yang mengalir dalam bahan/litar adalah berkadar terus dengan voltan yang digunakan (V) dan berkadar songsang dengan rintangan (R)) Formula Where: V = Voltage (V) I = Current (A) R = Resistance (Ω) Graph i. Linear Resistance Voltage (V) versus Current (I) in constant resistance ii. Non-Linear Resistance Voltage (V) versus Current (I) in non-constant resistance 1.4 Electric Power Definition The rate of electric energy transferred by an electric circuit, in amount of time Formula Where: Quantities Symbol Unit Power P = Watt (W) Current I = Ampere (A) Voltage V = Volt (V) Resistance R = Ohm (Ω) Work W = Joule (J) Time t = seconds (s) Electric charge Q = Coulomb (C) Derivation By using Ohm’s Law, it can derive new equation for electric power P = = = IV
1.5 Electric Energy Definition Energy which is converted from electrical potential energy Supplied by the combination of electric current and electrical potential that is delivered by the circuit Formula Where: Quantities Symbol Unit Electric energy T = kilo watt hour (kWh) or E Joule (J) Power P = Watt (W) Time t = seconds (s) Voltage V = Volt (V) Current I = Ampere (A) Resistance R = Ohm (Ω) Derivation By using electrical power formula and time, it can derive new equation for electric energy Relationship between electric energy and heat energy When the current flow, electron in the conductor will repel each other and it will produce heat and thus causing the cable that is used heating up i. Electric energy to heat energy ~ Oven and heaters, convert electric energy into thermal energy ii. Heat energy to electric energy ~ Burning of fossil fuels (oil, coal or natural gas) generates electric energy
1.6 Series and Parallel Circuits Series Circuit Parallel Circuit Connection of the resistor in the circuit The resistors is connected from end to end (provides only one path for current between two points) Series analysis are going determine total resistance, circuit current and total voltage Connection of the resistor which is against between each other Provides more than one path for current Each parallel path in a circuit is called a branch Parallel analysis are also going determine total resistance, circuit current and total voltage Total series resistance, RT is the sum of all resistor which exist in the circuit Total parallel resistance, RT Current is the same through all points Current through every resistor is equal to the total current, I T Total current, I T is equal to the sum of all current for each branch Total voltage, VT is the sum of all voltage drops across every resistor in the circuit The voltage across each parallel resistor is equal to the source voltage, VT Voltage Drop Reduction of the voltage supply in every resistor Can be calculate using: i. Ohm’s Law ii. Voltage Divider Law Current Divider Law VX = IT . RX VX = VT RX RT
1.7 Kirchoff’s Law 1 st Kirchhoff’s Law / Kirchhoff’s Current Law 2 nd Kirchhoff’s Law / Kirchhoff’s Voltage Law Currents entering the node equals currents leaving the node The sum of all the voltage drops around the loop is equal to zero V T - V 1 - V 2 - V 3 = 0 Units Conversion Units Prefix Table Prefix Symbol Prefix Prefix factor Multiplication Factor T tera 1012 1,000,000,000,000 G giga 109 1,000,000,000 M mega 106 1,000,000 k kilo 103 1,000 h hecto 102 100 da deka 101 10 d deci 10-1 0.1 c centi 10-2 0.01 m milli 10-3 0.001 μ micro 10-6 0.000,001 n nano 10-9 0. 000,000,001 p pico 10-12 0. 000,000,000,001 I 1 + I 2 + I 3 = I 4 + I 5 V T = V 1 + V 2 + V 3