ix Hands-On Lab Activities Each chapter includes labs that provide students with the practice to master application and are aligned with the chapter content. Labs include an objective, intro- duction, equipment list, procedures, and lab ques- tions. The Objective informs the student of the goal of the lab and what they will be practicing and learn- ing. Introduction provides an overview and key infor- mation useful for understanding the lab. Equipment lists the materials that a student will need to perform each lab successfully. Procedures offer step-by-step instructions to complete the lab. Lab Questions direct students in considering the main takeaways from each lab. End-of-Chapter Content End-of-chapter material provides an opportunity for review and application of concepts. A concise Summary provides an additional review tool and reinforces key learning objectives. This helps you focus on important concepts presented in the text. Know and Understand questions enable you to dem- onstrate knowledge, identification, and comprehen- sion of chapter material. Critical Thinking questions develop higher-order thinking and problem solving, personal, and workplace skills. 53 Copyright Goodheart-Willcox Co., Inc. Name __________________________________________ Date _______________________ Class ______________________ This multi-part lab will use hands-on application to build upon the lessons learned in this chapter. Its purpose is to give you practice in verifying Ohm’s law calculations by using a power source, loads, and a multimeter. Lab Introduction There will be three parts to this lab. This first part will use a battery and two different value resistors to compare calculated values to measured values. Since most HVACR meters only measure dc microamperes, large value resistors must be used with a 9 V battery. The second part includes observing and evaluating measured values. The third part of this lab uses 24 Vac and power resistors to compare calculated values to measured values. The 24 Vac allows for the use of an ac inductive clamp ammeter. Both the second and third lab will use a step-down transformer to supply approximately 24 Vac, which is called the second- ary voltage. This secondary voltage is a reduced voltage that is produced when the step-down transformer plugs into a 120 V. Use the lab diagrams to construct the circuits. The equipment below contains the materials for all three parts of the lab. Equipment • 1—Digital multimeter with clamp-on ammeter • Lab board. See Lab 3.2 for complete instructions. • 1—100,000 Ω 1/4 W resistor (no less than 5% tolerance) • 1—200,000 Ω 1/4 W resistor (no less than 5% tolerance) • 1—9 V dry cell battery • 2—60 W incandescent bulb • 16 or 14 AWG solid wire • 14 AWG wire nuts • 14 AWG spade terminals • 25 Ω 25 W power resistor • 50 Ω 25 W power resistor • 2—jumper wires with alligator clips Lab 4.1 Verifying Ohm’s Law through Simple Circuits Goodheart-Willcox Publisher Step-down transformer Bulb socket Terminal block Fuse 2 × 4 switch box Pictorial Diagram Figure 4.1-1. , 54 Copyright Goodheart-Willcox Co., Inc. Resistors Resistors are rated by ohmic value, tolerance, and wattage. A 10 Ω, 1/4 W resistor burns if 6 V are applied because the current 0.6 A (6 V/10 Ω) multiplied by the voltage of 6 V results in 3.6 W. A 1/4 W (0.250 W) resistor is too small for the application. The correct wattage resistor must be used by first calculating the resistor power consumption. Safety Note Procedure—Part One 1. Review Figure 4.1-2. 2. Connect one jumper end to the positive terminal of the battery and the other end to one end of the 100,000 Ω resistor. 3. Connect a second jumper to the negative end of the battery and the end to the opposite end of the 100,000 Ω resistor. 4. Measure and record the battery voltage (after resistor is connected). 5. Connect the 200,000 Ω resistor to the battery. 6. Measure and record the battery voltage (after resistor is connected). 7. Rewire circuit to include ammeter in circuit. See Figure 4.1-3. 8. Connect jumper to positive battery terminal and meter positive probe. 9. Connect jumper to negative meter probe and any one side of resistor. 10. Connect jumper to opposite side of resistor and to the negative battery terminal. 11. Complete Lab Questions for the 100,000 Ω resistor. 12. Replace the resistor with the 200,000 Ω resistor. Goodheart-Willcox Publisher Figure 4.1-2.. Goodheart-Willcox Publisher Figure 4.1-3.. Continued Cop ight G cox Fig 2 F 3 58 Copyright Goodheart-Willcox Co., Inc. Lab Questions Use your digital multimeter or other electrical instruments to answer the following questions. 1. What is the secondary voltage? ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ 2. Using the actual secondary voltage and the 25 Ω resistor, calculate the current. ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ 3. With only the 25 Ω resistor connected to the secondary, plug in the transformer and use the inductance clamp ammeter to measure the actual current draw of the resistor. Record value. ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ 4. Are the calculated and measured values of current approximately the same? ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ 5. Repeat the above steps using the 50 Ω resistor. Do the measured values support Ohm’s law? ______________________________________________________________________________________________________________ Know and Understand ____________ 1. Ohm’s law states a relationship between _____. A. voltage, resistance, and current B. volts, resistance, and current C amperes, volts, and ohms D. resistance, voltage, and amperes ____________ 2. Th e _____ is the unit of measure for voltage. A. EMF B. ohm C. ampere D. volt ____________ 3. Th e _____ is the unit of measure for current. A. ohm B. ampere C. volt D. intensity ____________ 4. Th e _____ is the unit of measure for resistance. A. ohm B. ampere C. volt D. watt ____________ 5. True or False? Resistance limits the current fl ow in a circuit. ____________ 6. Voltage is directly proportional to _____. A. resistance B. power C. current D. amperes