PASCO EM-8812 Resistance Apparatus - Manual (Page 7)

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M o d e l N o . E M - 8 8 1 2 E x p e r i m e n t 1 : E x p l o r a t o r y St u d y o f R e s i s t a n c e
7
Experiment 1: Exploratory Study of Resistance
Theory
Ohm’s Law describes the relationship between the resistance (R) of a wire, the volt-
age drop across it (V), and current through it (I):
(eq. 1-1)
In this experiment, you will apply a known current and measure V to determine R for
wires of various lengths, diameters, and materials.
Setup
1. Select the next-to-smallest brass wire (about 0.081 cm diameter). If you have a
micrometer, measure the diameter precisely.
2. Install the wire in the apparatus (see “Wire Installation” on page 5).
3. Connect the galvanometer sensor or voltmeter to the reference (-) and slider (+)
probes of the apparatus.
4. Position the reference probe at the 0 cm mark and the slider probe at the 24 cm
mark.
5. Connect the power supply to the power jacks of the apparatus so that current will
flow from right to left through the wire.
6. If you are using a separate current meter, connect it in series with the power sup-
ply and apparatus.
7. Turn up the power supply’s voltage until the current is about 1 A.
Part A: Resistance Versus Length
1. Measure V and I. Use Equation 1-1 to calculate R.
2. In a table, record R and , the length of the wire (or the distance between the
probes).
3. Repeat steps 1 and 2 for equal to 20, 16, 12, 8, and 4 cm.
Make a graph of R versus . Is the relationship linear? Does the best-fit line pass
(approximately) through the origin? What does this tell you about the relationship
between R and ?
Equipment Required Part Number
Resistance Apparatus with wire set EM-8812
Power Supply PI-9877 or similar
Patch Cords (4mm banana plug) SE-7123
Galvanometer Sensor or voltmeter (to measure voltage) PS-2160, SE-9786A or similar
Current Meter (may be built into the power supply) SE-9786A or similar
Micrometer (optional) SE-7337
R V I
⁄
=