Download Lab: Current and Voltage in a circuit

Mini-lab: Resistors in Circuits—quanitifying current and potential differences
Part 1: Individual Resistance
Materials needed: DC Power Supply; Pasco Circuit Board; 1 resistor between 100  and 680 ; 3 wires,
either banana plug or alligator clip; Digital Multimeter with leads; LabQuest; Current Probe;
Step 1: Measure the resistor’s resistance: ____________________ (Is it within the 5% tolerance?)
Step 2: Create a complete loop (see the example up front)
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Make sure the power supply is turned off before continuing!
insert one end of a banana plug wire into the (+) terminal of the DC power supply; insert the
other end of that wire into the (-) end of the current probe.
Connect a banana plug or alligator clip wore to the (+) end of the current probe, and then the
other end of that wire to a spring on the circuit board that is in the same square as one end of a
resistor (but the other spring)
Insert one of a banana plug wire into the (-) terminal of the DC power supply; insert the other
end of that wire into a spring on the circuit board that is in a square occupied by the other end
of the resistor.
Blue supply:
Depress the blue selector button (on the left) for 0-24V DC, and make sure the “Volts” button on
the right is popped out.
Turn the voltage knob all the way to the left.
Grey Supply:
Turn both the current and the voltage knobs to the left. Note: When you turn it back on, you’ll
be adjusting the voltage—but you must turn the current knob a tiny bit to the right or it won’t
work at all.
Step 3: Data Collection
1. Set your multimeter to read DC Voltage (the symbol V with the straight line and dotted line over
the top). Make sure your red lead is in the appropriate port of the multimeter—it should be in
the port labeled with the V, which means you may need to change this from where it was when
you measured resistance.
2. For all data you will be reading the potential difference across the resistor, which means you
need to put the leads of the multimeter on either side of the resistor in the circuit. You will NOT
be recording the value from the power supply—that’s for your reference only.
Ready? 
3.
4.
5.
6.
7.
Turn on the power supply (the voltage should initially read 0); slowly change the voltage to 0.5 V
Measure the voltage drop across the resistor. Record in the table below.
Remove the leads, replace the white wire.
Repeat steps 4-7 for two more trials.
Remove the multimeter from the circuit. Slowly increase the voltage by 0.5 V using the knob on
the power supply. Important: Use no more than 5.0 V from the Power Supply!
8. Repeat steps 4-8 for the new voltage
9. Repeat steps 9-10 until you have filled in the data table.
Table 1: Measured Potential Drop Across and Current Through a Single Resistor
Resistor Used, measured resistance / 
Power
Supply
Reference
Voltage Drop Across Resistor / V
Trial 1
Trial 2
Trial 3
Current Through Resistor / x 10-3 A
Trial 1
Trial 2
Trial 3
*note: I’m minimizing the data you need by allowing only 6 manipulations. You are welcome to do
more, if time allows. If, however, any one of your data points is obviously an outlier, you MUST do
another trial—so keep your resistors and wires set up until you’ve done a rough draft of your graph.
Table 2: Average Voltage Drop and Currents Through a Resistor
Power
Supply
Reference
Voltage Drop Across
Resistor / V
Average
Uncertainty
Current Through Resistor /
x 10-3 A
Average
Uncertainty
Plot a graph to show your data. Please treat the current as the manipulated variable (even though it
didn’t look like that’s what you manipulated…trust me on this). Print out your graph, attach it to this
worksheet, and then complete the Post-Lab: Voltage and Current in WebAssign.