MARINE ELECTRO-TECHNIQUE 1

Chapter 1 LMD 13003 MARINE ELECTRO-TECHNIQUE 1 Chapter 2 Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 DC CIRCUIT Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Model of atom The Bohr atom is a tool for visualizing atomic structure. •The nucleus is positively charged and has the protons and neutrons. •Electrons are negatively charged and in discrete shells. •The atomic number is the number of protons and determines the particular element. •In the neutral atom, the number of electrons is equal to the number of protons. Electron Proton Neutron Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Atomic structure The outer shell is called the valence shell. Electrons in this shell are involved in chemical reactions and in metals they account for electrical and thermal conductivity. A neutral Si atom is shown. + Shell 1 Shell 2 Shell 3 There are 4 electrons in the valence shell. Is Si a conductor, insulator, or semiconductor? Semiconductor Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Force There is a force (F) between charges. Like charges repel; unlike charges attract. •The force is directly proportional to charge. •The force is inversely proportional to square of distance. + + _+ Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 • The force of attraction or repulsion between two charged bodies Q1 and Q2 can be determined by Coulomb’s Law: F = k Q1Q2 r2 • Where F is in Newtons (N), k a constant = 9.0109 Nm2 / C 2 • Q1 and Q2 are the charges in coulombs Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Voltage Voltage (V) is the energy (W) per charge (Q); it is responsible for establishing current. V =W + - Q + - + - Work is done as a charge is + - moved in the electric field + - from one potential to another. + - + - Voltage is the work per charge + - done against the electric field. + - Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Voltage Definition of voltage V =W Q One volt is the potential difference (voltage) between two points when one joule of energy is used to move one coulomb of charge from one point to the other. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Voltage Voltage Voltage is responsible for establishing current. Sources of voltage e- + e- include batteries, solar cells, and generators. A Zinc Copper Cu Cu-Zn battery, such as (anode) (cathode) you might construct in a chemistry class, is Zn2+ Zn + 2e- Cu2+ + 2e- shown. ZnSO4 CuSO4 solution solution Porous barrier Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Current Current (I) is the amount of charge (Q) that flows past a point in a unit of time (t). I=Q t One ampere is a number of electrons having a total charge of 1 C move through a given cross section in 1 s. What is the current if 2 C passes a point in 5 s? 0.4 A Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2Motion of negatively charged electrons in a copper wire when placed across battery terminals with a difference in potential of volts (V). Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Current (I) is the amount of charge (Q) that flows past a point in a unit of time (t). • Flow of electric charges – -ve charge (electron) flow to +ve terminal. – + ve charge flow to –ve terminal – This motion creates electric current • It is conventional to take the current flow as the movement of positive charge, that is opposite to the flow of electron. © Copyright 2006 Prentice-Hall Principles of Electric Circuits - Floyd

Chapter 2 Current • Electric current is the time rate of change of charge, measured in amperes (A) • 1A=1C/s • Direct current (dc): current that remains constant with time. • Alternating current (ac): current that varies sinusodally with time. i = dq dt i = current in ampere q= charge in coulomb t = time in second Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Current direct current Alternating current exponential current Damped current Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance • The flow of charge through any material encounters an apposing force similar in many respect to mechanical friction. • This opposition, due to the collision between electrons and between electron and other atoms in material, which converts electrical energy into heat, is called the resistance of material. • The unit of measurement of resistance is the ohm, for which the symbol is Ω. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance • The circuit symbol for resistance : • The resistance of any material with a uniform cross-sectional area is determined by the following factors: – Material – Length – Cross-sectional Area – Temperature Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance • At a fixed temperature of 20°C, the resistance is related to the other 3 factor by, R= l  A • Where; – ρ (Greek letter rho) is the characteristic of the material called resistivity, – l is the length of the sample – A is the cross-sectional area of the sample Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance • The higher the resistivity, the greater the resistance of conductor • The longer the conductor, the greater the resistance • The greater the area of a conductor, the less the resistance Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance: Temperature Effect • Temperature have a significant effect on the resistance of conductors, semiconductors and insulators. • Conductors – For good conductors, an increase in temperature will result in an increase in the resistance level. Consequently conductors have a positive temperature coefficient. • Semiconductor – For semiconductor materials, an increase in temperature will result in a decrease in the resistance level. Consequently, semiconductors have negative temperature coefficient. • Insulators = Semiconductors Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance: Temperature Effect • For a moderate range of temperature, such as 100°C, the change of resistance is usually proportional to the change of temperature; • The ratio of the change of resistance per degree change of temperature to the resistance of some definite temperature are called coefficient of resistance, α. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance Resistance is the opposition to limit current flow. One ohm (1 ) is the resistance if one ampere (1 A) is in a material when one volt (1 V) is applied. Conductance is the reciprocal of resistance. G= 1 R Components designed to have a specific amount of resistance are called resistors. Color bands Resistance material (carbon composition) Insulation coating Leads Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance Resistance value, first three bands: Color Digit Multiplier Tolerance First band-1st digit Black 0 10 0 Second band- 2nd digit Brown 1 101 1% (five band) *Third band- multiplier (number of Red 2 102 2% (five band) Orange 3 10 3 zeros following the 2nd digit) Yellow 4 10 4 Green 5 10 5 Blue 6 10 6 Violet 7 10 7 Gray 8 10 8 White 9 10 9 Fourth band- tolerance Gold ±5% 10 -1 5% (four band) Silver ± 10% 10 -2 10% (four band) No band ± 20% * For resistance values less than 10, 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. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance What is the resistance and tolerance of each of the four-band resistors? 5.1 k ± 5% 820 k ± 10% 47  ± 10% 1.0  ± 5% Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance Alphanumeric Labeling • Two or three digits, and one of the letters R, K, or M are used to identify a resistance value. • The letter is used to indicate the multiplier, and its position is used to indicate decimal point position. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistance Variable resistors include the potentiometer and rheostat. A potentiometer can be connected as a rheostat. The center terminal is connected to the wiper R 1 3 2 Variable (potentiometer) Shaft Wiper Resistive R element Principles of Electric Circuits - Floyd Variable (rheostat) © Copyright 2006 Prentice-Hall

Chapter 2 Basic Circuit A basic circuit consists of 1) a voltage source, 2) a transmission system and 3) a load 4) a control apparatus. An example of a basic circuit is the flashlight, which has each of these. Switch Metal strip Metal reflector Spring Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Basic Circuit Elements • One element on simple circuit is a mathematical model for electric apparatus that have two terminals. Basic Circuit Elements Active Elements Passive Elements ❖Could supplied power to ❖Only could absorb circuits power ❖Example : Voltage and ❖Example : resistor, Current source inductance, capasitance, diod and etc. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Voltage and Current Source • An ideal Independent source is an active element that provides a specified voltage or current that is completely independent of other circuit element • An Ideal Dependent source is an active element which the source quantity is controlled by another voltage or current. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Independent source Voltage Current Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Dependent source dependent voltage- dependent current- Controlled voltage controlled voltage source source dependent voltage- dependent current- controlled current source controlled current source Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 1. Ohm’s Law The most important fundamental law in electronics is Ohm’s law, which relates voltage, current, and resistance. Georg Simon Ohm (1787-1854) studied the relationship between voltage, current, and resistance and formulated the equation that bears his name. I =V R What is the current in from a 12 V source if the resistance is 10 ? 1.2 A Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Formula for voltage Ohm’s law If you need to solve for voltage, Ohm’s law is: V = IR What is the voltage across a 680  resistor if the current is 26.5 mA? 18 V Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Formula for resistance Ohm’s law If you need to solve for resistance, Ohm’s law is: R = V I What is the (hot) resistance of the bulb? 132  115 V Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 The linear relationship of Current and Voltage Graph of Current versus Voltage Notice that the plot of current versus voltage for a fixed resistor is a line with a positive slope. What is the resistance indicated by the graph? 2.7 k What is its conductance? 0.37 mS Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Graph of Current versus Voltage • R constant Increase V, I increase I =V R I = V Decrease V, I decrease R Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Graph of Current versus Resistance If resistance is varied Current (mA) 10 for a constant voltage, 8.0 the current verses 6.0 1.0 2.0 3.0 resistance curve plots a 4.0 Resistance (k) hyperbola. 2.0 What is the curve for 0 a 3 V source? 0 Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Graph of Current versus Resistance • V constant I = V Increase R, I decrease R I = V Decrease R, I increase R Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Application of Ohm’s law 26.8 mA The resistor is green-blue brown-gold. What should the ammeter read? Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 1n 2. Energy Energy, W, is the ability to do work and is 1m measured in joules. One joule is the work done when a force of one newton is applied through a distance of one meter. The symbol for energy, W, represents work, but should not be confused with the unit for power, the watt, W. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Power Power is the rate energy is “used” (actually converted to heat or another form). Power is measured in watts (or kilowatts). Notice that rate always involves time. One watt = one joule/second Power = Energy time or P= w t Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Power in electric circuit Power Three equations for power in circuits that are collectively known as Watt’s law are: P = IV P = I2R P = V2 R Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Power Example 2.5 Calculate the power in each of three circuits below: 2A 2A 47 Ω 5V 10 Ω 10 V V (a) (b) (c) Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Power Resistor Power Rating • A resistor gives off heat when there is current through it. • There is a limit to the amount of the heat that a resistor can give off, which is specified by its power rating. • The power rating is the maximum amount of power that a resistor can dissipate without being damaged by excessive heat buildup. • The power rating is not related to ohmic value (resistance) buut rather determined by the physical size and shape of the resistor. • The larger the surface area of resistor, the more power it can dissipate Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Power How to select the proper power rating for an application • When a resistor is used in circuit, its power rating must be greater than the maximum that it will have to handle. • For example, if a carbon-composition resistor is to be dissipate 0.75 W in a circuit application, its rating should be at least next higher standard value which is 1 W. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Resistor failures Resistor failures are unusual except when they have been subjected to excessive heat. Look for discoloration (sometimes the color bands appear burned). Test with an ohmmeter by disconnecting one end from the circuit to isolate it and verify the resistance. Correct the cause of the heating problem (larger resistor?, wrong value?). Normal Overheated Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Power Example 2.8 Determine whether the resistor in each circuit below has possibly been damaged by overheating. ¼W ½W 100 Ω 62 Ω 9V V Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 Series circuits All circuits have three common VS + R1 R2 attributes. These are: R3 1. A source of voltage. 2. A load. 3. A complete path. A series circuitis one that has only one current path. Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 • Two types of current are readily available, direct current (dc) and sinusoidal alternating current (ac) • We will first consider direct current (dc) • The direction of conventional flow ( Iconventional) is a opposite to that of electron flow ( Ielectron). Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall

Chapter 2 • By following the direction of conventional flow – There is a rise in potential across the battery (- to + ) – Drop in potential across the resistor ( + to - ) Principles of Electric Circuits - Floyd © Copyright 2006 Prentice-Hall