Fat: Who Says? Measuring Obesity by Bioelectrical Impedance Analysis Circuitous Adventures- Length of Conductors vs. Resistance Student Information Page 3C Part D Activity Introduction: In this activity, you will be investigating the relationship between the length of an electrical conductor and its resistance. Activity Background: Pencil lead is not really made up of the element called lead. It is made of a crystalline form of pure carbon called graphite. Diamonds are another form of crystalline carbon. Not all pure carbon can conduct electricity. Experimental Design Basics An experiment is designed to search for cause and effect relationships. An experiment that is well-designed will change one factor (cause) in a very specific way to see if another factor responds (effect) to the change. The factors that are changed in this way are called variables. There are three types of variables in an experiment: independent, dependent, and constants (controlled). The independent variable in an experiment is the variable that is manipulated or changed by the experimenter. Thus, it is sometimes called the manipulated variable. A good experiment can only have one independent variable. In this experiment, think about what will be different about the graphite stick in each test group? The dependent variable is the factor observed to see how it responds to the independent variable. It is also called the responding or outcome variable. Think about what may respond as you change the length of the graphite stick. Constants are things that are kept the same in each test group of an experiment. In order to have a controlled experiment, all variables except the independent and dependent variables must be controlled. This is done by making sure that they are the same for all test groups. In a good experiment, scientists must be able to measure the variables. Length, distance, and mass are easy to measure. Sweetness in foods or love are not as easy to measure. In planning an experiment, it must be determined how you will measure the variables in your experiment. 36Corpulosity
Identify Variables: Independent Variable: Dependent Variable: List 3 variables that must be made constant in this experiment. a. b. c. State Your Hypothesis: Write a hypothesis that predicts how the independent variable may affect the dependent variable. Be sure to write the hypothesis as an if, then statement and explain why you think this will happen. Hypothesis: Activity Materials: (per student or station) 1 Graphite stick 1 Analog multimeter 1 Metric ruler 1 Simple Circuit (see Part C of this activity) 1 Copy Student Information Page 1 Copy Student Data Page 37Corpulosity
Activity Instructions: 1. Before doing this part of the activity, be sure you know how resistance is measured in a circuit. If you have questions, review the Instruction Cards 1, 2, and 3. 2. Set your multimeter dial (function selector) on the proper setting to measure resistance. 3. Use the multimeter to measure the resistance across the entire length of the graphite stick. Record the length and resistance in Length vs. Resistance Data Table. Repeat this step a second time to ensure accuracy in measurement. 4. Then place one of the alligator clips of the multimeter on one end of the graphite stick. Place the other clip 4 cm from the end of the graphite stick so you are measuring only part of the full length of the graphite. Measure and record the resistance across that portion. 5. Repeat step 4 reducing the length of graphite stick being measured by 4 cm until you reach the last 4 cm of the graphite. Measure and record the resistance across that portion. Activity Results: Length vs. Resistance Data Table Length (cm) Resistance 1 (Ω) Resistance 2 (Ω) Average Resistance (Ω) 38Corpulosity
Graph: Make a graph of your data. Be sure to include a title, axis labels, and units of measurement. Title (Axis label) (Axis label) 39Corpulosity
Processing Out: 1. Explain in a list of steps (a procedure) how you used the multimeter and metric ruler to determine if there is a relationship between length of a conductor and the resistance. 2. Using the data you collected, explain the relationship between length and conductivity (resistance.) 3. Do you accept or reject your hypothesis? Explain. (Hint: Explain how the data support your hypothesis or do not support it.) 4. Do you think that the relationship you have found would also be true for metal wires? Why or why not? Corpulosity 40
Conduct an experiment to test the hypothesis you just made. You may use materials from previous parts of this activity as needed, or you can use various metal items in the room. Your Hypothesis: Your Materials: Your Procedure: 41Corpulosity
Your Data: (Data Table here) Your Conclusions: 42Corpulosity