Download Lab : Exploring Voltage, Current, and Resistance

Names_________SAMPLE ANSWERS_______/______________Period____ Lab : Exploring Voltage, Current, and Resistance
Objectives:
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To learn the proper use of digital instruments to accurately measure voltage, current,
and resistance in an electric circuit.
To determine the relationship of voltage, current, and resistance in an electric circuit
In this lab activity you will use a Digital Multimeter (DMM) to measure voltage, current, and resistance in different sections of an electric circuit. You will see how the flow of current and the voltages are distributed around the circuit. You will then compare your results to values predicted by Ohm’s Law (V=IR). Each student in the lab group will have a slightly different circuit to build and measure. PRE‐LAB VIDEO TUTORIALS and ON‐LINE QUIZ At home, on your own time, you must watch the following three videos about the proper use of a digital multimeter. After viewing the videos, you must take and pass (70%+) the on‐line Pre‐Lab Quiz prior to starting the lab. These must be completed before the day of the activity. Videos: 
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Measuring Voltage with a Digital Multimeter http://tinyurl.com/mrchan‐voltmeter Measuring Current with a Digital Multimeter http://tinyurl.com/mrchan‐ammeter Measuring Resistance with a Digital Multimeter http://tinyurl.com/mrchan‐ohmmeter Prelab Quiz : ____________________________________
EQUIPMENT & SUPPLIES
 6 Volt battery pack or power supply  Digital Multimeter (Cen‐Tech, Fluke, or other brand)  4 connecting wires with alligator clip leads  Type #46 6‐volt flashlight bulb and socket  4 Resistors of different values 1 Lab: Exploring Voltage, Current and Resistance IISME Names_________SAMPLE ANSWERS_______/______________Period____ + A1 Ammeter
R1 R1 + VR1 battery + A2 + Vbat Voltmeter Bulb R2 BASIC CIRCUIT Bulb R2 + VR2 + A3 BASIC CIRCUIT with MEASUREMENT POINTS + V Voltmeter + A Ammeter
ASSEMBLING and TAKING MEASUREMENTS OF THE CIRCUIT The basic circuit is the same however, each student will choose and use a different resistor R1. There should be 4 different resistors to choose from, with different markings on them. Be sure to note the markings on the resistor you are using, and do not mix it up with your partners’ because your measurements will be different. The markings may be either colored bands (“black‐yellow‐black‐gold”) or small digits (“2215”). The first student should assemble the circuit as shown in the schematic on the left. Then, using the Digital Multimeter in the three different modes, measure the voltages, currents, and resistances as shown in the schematic at right. If you do not know how to use the DMM, view the assigned video tutorials or ask a partner. It is more efficient to take all the voltage measurements first, then change the mode of the DMM to take all the current measurements and then resistance measurements. Each student, in turn, should construct the circuit with his/her own resistor and take measurements. It should go quickly after the first measurements are made. Your partners may offer instruction and advice, but are not allowed 2 Lab: Exploring Voltage, Current and Resistance IISME Names_________SAMPLE ANSWERS_______/______________Period____ to construct or take your measurements for you. Each student should record results and calculations on his/her own worksheet. After all students have completed the measurements and calculations, combine all results into a single worksheet to turn in. Write the equation that relates the Resistance R of a resistor to the Current I and Voltage V . If you don’t remember it, look in your notes. R=V/I
Write the equation that relates the Power P to the Current I and Voltage V in a resistor. If you don’t remember it, look in your notes. P=IxV
Calculating Percentage Difference between Measured vs. Calculated values %
100% YOUR RESISTOR ID: Note the markings or color bands (e.g., “Brown‐Black‐Red‐Gold” , or “2215”) of your resistor. Do not mix it up with your partners’ resistors! DATA TABLE – Student 1’s MEASUREMENTS & CALCULATIONS STUDENT #1 NAME Joe Student
RESISTOR ID Markings Red-Red-Black-Gold
VOLTAGE Measured VR1 3.3 V
VR2 2.35 V
CURRENT Measured I1 0.16 A
I2 0.16 A
RESISTANCE Measured R1 23 Ohms
R2(bulb) 13 ohms
RESISTANCE Calculated R1 20.6 Ohms
R2(bulb) 14.7 Ohms
POWER Calculated P1 0.53 W P2(bulb) 0.38W
%Diff Resistance R1 %diff should be less
R2 %Diff
than 15%
Calc. vs. Measured DATA TABLE – Student 2’s MEASUREMENTS & CALCULATIONS STUDENT #2 NAME RESISTOR ID Markings VOLTAGE Measured VR1 VR2
CURRENT Measured I1 I2
RESISTANCE Measured R1 R2(bulb)
RESISTANCE Calculated R1 R2(bulb)
POWER Calculated P1 P2(bulb)
%Diff Resistance R1 %diff R2 %Diff
Calc. vs. Measured 3 Lab: Exploring Voltage, Current and Resistance Vbattery 5.65 V
I3 0.15 A ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ Vbattery I3 ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ IISME Names_________SAMPLE ANSWERS_______/______________Period____ DATA TABLE – Student 3’s MEASUREMENTS & CALCULATIONS STUDENT #3 NAME RESISTOR ID Markings VOLTAGE Measured VR1 VR2
CURRENT Measured I1 I2
RESISTANCE Measured R1 R2(bulb)
RESISTANCE Calculated R1 R2(bulb)
POWER Calculated P1 P2(bulb)
%Diff Resistance R1 %diff R2 %Diff
Calc. vs. Measured DATA TABLE – Student 4’s MEASUREMENTS & CALCULATIONS STUDENT #4 NAME RESISTOR ID Markings VOLTAGE Measured VR1 VR2
CURRENT Measured I1 I2
RESISTANCE Measured R1 R2(bulb)
RESISTANCE Calculated R1 R2(bulb)
POWER Calculated P1 P2(bulb)
%Diff Resistance R1 %diff R2 %Diff
Calc. vs. Measured Vbattery I3 ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ Vbattery I3 ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ ‐‐‐‐‐‐‐ GROUP DISCUSSION & ANALYSIS 1. How do the currents I1, I2, and I3 compare. Is there a significant (10% or more) difference? If so, explain which current is greater and why. The currents are approximately the same at all points in the series circuit 2. Look closely at the voltage measurements. Describe and Explain the relationship between the voltages VR1 and VR2 across R1 & R2 (bulb) compared to the battery voltage Vbattery The voltages Vr1 and Vr2 are both less than Vbattery (OK answer)
The sum of Vr1 and Vr2 is equal to Vbattery (Better answer) 3. What are some reasons that the measured vs. calculated resistances are different? NOTE: “Human Error” is an unacceptable response and will result in 10% grade reduction. 1) The leads of the meter have approximately 1 to 3 ohms of resistance by themselves
2) The light bulb resistance changes when it heats up 4 Lab: Exploring Voltage, Current and Resistance IISME