Fat: Who Says? Measuring Obesity by Bioelectrical Impedance Analysis Circuitous Adventures-Measuring Electrical Values Student Information Page 3C Part B Activity Introduction: Surge ahead and learn how to use a multimeter device to measure voltage, amps, and resistance. Resistance is futile! Activity Background: Whenever charged particles are taken from one object and given to another object, an imbalance of charge occurs. This imbalance of charge is called voltage (or potential difference). Voltage is measured in units called Volts (V), named after Alessandro Volta. An electric current is nothing more than the flow of electric charges from one location to another. The measure of how much flow is occurring at any given point is called the amperage and is measured in units called amps (A), named after André-Marie Ampère. Electric charges can only flow through certain materials, called conductors. Materials that resist the flow of current are called insulators. Materials offer resistance to the flow of current. This resistance is measured in units called ohms (Ω), named after its discovered Georg Ohm. Ohm’s law states that the amount of current (I) flowing through a conductor times the resistance (R) of the conductor is equal to voltage (V) of the source of power (i.e. batteries). This law is often expressed in the following form:
V = I X R
Note: V = voltage, I = current, and R = resistance Activity Materials: • 2 batteries • 1 battery holder • Several electrical wires (stripped) or with alligator clips • 1 buzzer • 1 switch • 1 Analog multimeter • 1 Copy Student Information Page • 1 Copy Student Data Page • Transparency of Figure 3 Part B
LESSON 3
® Positively Aging /M.O.R.E. ACTIVITY 3C, PART B Corpulosity 2007©The University of Texas Health Science Center at San Antonio 29 Activity Instructions: 1. Before doing anything, you must familiarize yourself with the use of the multimeter that has been provided for you. To do this you need to complete Instruction Cards 1, 2 and 3. Your teacher must check your answers before you continue with this lab. 2. Using the same equipment you used in Part A of this activity, recreate the simple circuit you made. Make sure all devices are placed exactly as they were. Use your drawing to accomplish this task. (If you did not complete Part A, see the instructions in Part A to set up a simple circuit). 3. Using the multimeter, measure the following values: i) DC voltage across the batteries ii) DC current in the circuit between the batteries and the buzzer, iii) DC resistance across the buzzer. 4. For accuracy, repeat each of these measurements and average them. Record your information in the Data Table 1 below or create a data table on your own paper. 5. Remember, when using the multimeter you need to have the switch on to take these readings. Be sure top turn the switch off when you have finished with the meter. 6. Represent DC voltage, DC current, and DC resistance by recreating your drawing from Part A. This time, add the placement of the multimeter (position of the multi- meter in the circuit) as it is used to measure each value. Then create a chart and record the voltage, current and resistance at the locations indicated in step 3 above. [Hint: Look at Transparency labeled Figure 2].
Processing Out: Data Table 1 – Voltage, Current, and Resistance Voltage Current Resistance Trial #)1 (V) (mA) (Ω)
1
2
Average
LESSON 3
® Positively Aging /M.O.R.E. ACTIVITY 3C, PART B Corpulosity 2007©The University of Texas Health Science Center at San Antonio 30 1. The relationship of voltage, current, and resistance can be expressed in a mathematical way in a formula that represents Ohm’s law (V = I X R). Try putting the current and resistance you measured into the equation to see if your answer (the voltage) is the same as the voltage you measured. How is Ohm’s Law represented in the measurements you made? ______
2. What factor(s) might cause the numbers you recorded for your circuit to be different than what you would expect in the Ohm’s Law relationship? ______
LESSON 3
® Positively Aging /M.O.R.E. ACTIVITY 3C, PART B Corpulosity 2007©The University of Texas Health Science Center at San Antonio 31