Week 2 - EEM107 - Voltage and Circuit Concepts PDF

Chapter 3 Voltage Objectives  After completing this chapter, you will be able to:  Identify the six most common voltage sources  Describe six 6 different methods of producing electricity  Define a cell and a battery  Describe the difference between primary and...

Chapter 3 Voltage Objectives  After completing this chapter, you will be able to:  Identify the six most common voltage sources  Describe six 6 different methods of producing electricity  Define a cell and a battery  Describe the difference between primary and secondary cells  Describe how cells and batteries are rated  Identify ways to connect cells or batteries to increase current or voltage output or both  Define voltage rise and voltage drop  Identify the two types of grounds associated with electrical circuits  Voltage Sources  Six common voltage sources:  Friction, magnetism, chemicals, light, heat, and pressure  Friction  Oldest known method of producing electricity  Example: Van de Graaf generator  Van de Graaf generator https://youtu.be/3Ptu07enIsY https://www.youtube.com/watch?v=y20lKZB5BR0 Voltage Sources (cont’d.)  Magnetism  Most common method used today  Example: generator  Chemical cell  Second most common method used today  Contains positive and negative electrodes separated by an electrolytic solution  Electromagnetic Generators https://www.youtube.com/watch?v=WhATjUHgzxQ  Voltage Sources (cont’d.) Figure 3-6. A photovoltaic cell can convert sunlight directly into electricity.  A photovoltaic (Solar) Cells https://www.youtube.com/watch?app=desktop&v=UJ8XW9AgUrw SciToons channel, Brown University, USA  Voltage Sources (cont’d.) Figure 3-8. Thermocouples convert heat energy directly into electrical energy (commonly used to measure directly temperature in ovens, stove…etc.) Note: This shows that the conversion of energy from Thermal energy (Heat) to Electrical Energy. However, is not widely use to generate electric power! Cells and Batteries  Battery  Combination of two or more cells  Primary cells  Cannot be recharged  Example: dry cells  Secondary cells  Can be recharged  Example: lead-acid, Lithium-ion batteries Connecting Cells and Batteries  Series-aiding configuration  Output current is the same IT = I1 = I2 = I3  Output voltage increases ET = E1 + E2 + E3 Connecting Cells and Batteries (cont’d.) Figure 3-18. Cells or batteries can be connected in series to increase voltage. Connecting Cells and Batteries (cont’d.)  Parallel configuration  Output current increases IT = I1 + I2 + I3  Voltage output remains the same ET = E1 = E2 = E3 Figure 3-19. Cells or batteries can be connected in parallel to increase current flow. Connecting Cells and Batteries (cont’d.) Figure 3-20. Cells and batteries can be connected in series-parallel to increase current and voltage outputs. Connecting Cells and Batteries (cont’d.) Figure 3-21. The voltage increases when cells are connected in series.  Connecting Cells and Batteries (cont’d.) Figure 3-22. Connecting the series-connected cells in parallel increases the output current. The net result is a series-parallel configuration.  Voltage Rises and Voltage Drops Figure 3-23. A potential applied to a circuit is called a voltage rise. Figure 3-24. The energy used by the circuit in passing current through the load (resistance) is called a voltage drop. A voltage drop occurs when current flows in the circuit. Ground as a Voltage Reference Level  Ground  Term used to identify zero potential  Earth grounding In the home, all electrical circuits and appliances are earth grounded. Consequently,  Keeps appliances and equipment at same potential no difference of potential exists between any two appliances to avoid electrocution/electric  Electrical grounding shocks  Provides common reference point Electrical grounding is used in automobiles. Here the chassis of the automobile is used as a ground. This can be verified by seeing where the battery cables are attached to the automobile. Generally, the negative terminal is bolted directly to the frame of the automobile. This point or any other point on the frame of the automobile is considered to be ground. Ground serves as part of the complete circuit  Summary  Current is produced when an electron is forced from its orbit  Voltage provides energy to dislodge electrons from their orbit  A voltage source provides a means of converting some other form of energy into electrical energy  Cells and batteries can be connected in series, in parallel, or in series-parallel to increase voltage, current, or both  Key concepts in this chapter:  Primary cells, secondary cells, ampere-hours, voltage rise, voltage drop, Ground Chapter 4 Resistance Objectives  After completing this chapter, you will be able to:  Define resistance and explain its effect in a circuit  Determine the tolerance range of a resistor  Identify carbon composition, wirewound, and film resistors  Identify potentiometers and rheostats  Describe how a variable resistor operates  Decode a resistor’s value using the color code or alphanumeric code  Identify the three types of resistor circuits  Calculate total resistance in series, parallel, and series- parallel circuits Resistance  Conductance (R)  Ability of a material to stop/hinder electrons flow.  Unit of Resistance in Ohm, [Ω] Figure 4-1. Resistance of several conductors of the same length and cross-section area A. Conductance  Conductance (G)  Ability of a material to pass electrons: inverse (1/x) of Resistance  Unit of conductance is Mho (mirror of the word Ohm)  Measured in Siemens (S)  Resistors  Resistors  Elements of electrical and electronic circuits  Possess a specific value of resistance to current flow  Have values of their resistance in in Ohm, [Ω]  They can be: Either fixed (changeable) or Variable (non-changeable)  Resistor’s tolerance (variance due manufacturing variability)  Their values can vary and still be acceptable within a range called tolerance range  10% tolerance is satisfactory, generally.  Resistors (cont’d.) Figure 4-6. Carbon composition resistors were the most widely used resistors in electronic circuits. The wirewound resistor is constructed of a nickel- chromium alloy (nichrome) wire wound on a ceramic form (Figure 4-7). Leads are attached and the entire resistor is sealed with a coating. Wirewound resistors are used in high-current circuits where precision is necessary. The resistance range varies from a fraction of an ohm to several thousand ohms. Figure 4-7. Wirewound resistors are available in many different styles.  Resistors (cont’d.) Figure 4-8. The film resistor offers the size of the carbon resistor with the accuracy of the wirewound resistor. Film resistors have become popular (Figure 4-8) because they offer the small size of the composition resistor with the accuracy of the wirewound resistor. A thin film of carbon is deposited on a cylindrical ceramic core and sealed in an epoxy or glass coating to form a carbon film resistor Figure 4-10. Variable resistors allow the resistance to increase or decrease at random.  Resistors (cont’d.)  Potentiometer (or pot)  A variable resistor used to control voltage (small currents)  Used in audio volume and tone controls, lighting dimmer switches, and motor speed control in robotics.  Rheostat  A variable resistor used to control current (large currents)  Used to control motor speed, heat, and voltage in electronic circuits. Figure 4-12. The Electronic Industries Association (EIA) 4-band color code. Resistor Value Identification using Electronic Industries Association (EIA) 4 and 5-band color code 3RD DIGIT Figure 4-13. Meaning of the colored bands on a carbon composition resistor. R=[1ST Digit] [2ND Digit2]10^[[3RD Digit] ± TOLERANCE% Resistor Value Identification using Electronic Industries Association (EIA) 4 and 5-band color code The brown band (first band) represents the 1st digit (=1) The green band (second band) represents the 2nd digit (=5) The red band (third band) represents 3rd digit (=2) The silver band (fourth band) indicates a resistance tolerance of 10%. Therefore, this is a R=15.102 = 1500ohm with a ±10% tolerance, which means can take any value between R=1500-10%x1500 and R=1500+10%x1500 Resistor Value Identification using Electronic Industries Association (EIA) 4 and 5-band color code (i.e. exponent) The fifth band on a resistor indicates the resistor’s reliability. Reliability of the resistor tells how many of the resistors (per thousand) will fail after 100 hours of operation (Quality indicator) Electronic Industries Association (EIA) 5-band color code Resistor Value Identification: Alfa-Numerically Figure 4-16. Resistors may also be identified by a letter- and-number system. RN60D5112F has the following meaning: RN60 Resistor style ( composition, wirewound, film) D Characteristic (effects of temperature) 5112 Resistance value (2 exponent, i.e., # of zeros) F Tolerance (1%) Therefore, this resistor of R=[511.102 ±1%x 511.102]Ω Figure 4-18. Three types of resistive circuits: (A) serial circuit, (B) parallel circuit, (C) serial-parallel circuit. Connecting Resistors in Series  Series circuit  Provides one path for current to flow  Total resistance formula: RT = R1 + R2 + R3 … + Rn Connecting Resistors in Parallel  Parallel circuit  Provides two or more paths for current to flow  Total resistance formula: 1/RT = 1/R1 + 1/R2 + 1/R3 … + 1/Rn  Total resistance is always less than smallest resistor Connecting Resistors in Series and Parallel  Series-parallel circuit  Combination of a series and a parallel circuit  To calculate total resistance, use the series and parallel formulas  Summary  Resistance is opposition to flow of current  Several factors, such as size and type of wire, affect electrical resistance  Resistors are either fixed or variable  Three major categories of resistors:  molded carbon composition, wirewound, or film  Variable resistors allow resistance to vary/change  Resistor values may be identified by colored bands or by an alphanumeric system  Three types of resistive circuits: series, parallel, series-parallel