Download Resistance of Coils

Resistance (and more!) of wires…
When we dissected the motor, you may have seen the thin wire wrapped around
the three iron cores. What can we learn about electricity with a simple wire?
YOU CAN USE THIS DOCUMENT AS A GUIDE, BUT record all data and include
sketches and/or photos of your setup so that it is all in one clear document.
Part 1—measuring resistances in a (long) coil of wire
1. Cut a long length of thin magnet (enameled) wire—at least 15-30 m long!
2. Make a mark or add a piece of tape about 1/3 and 2/3 of the length of
wire.
3. Wrap three loops (but without breaking the wire). You can wrap around
your hand or a small bottle or even a white board marker. Use a piece of
tape to keep each of the loops from unraveling.
4. Carefully sand off the enamel at the ends of the wire and at the places
where you have placed the tape.
5. Use a multimeter as an ohmmeter to measure the following resistances:
RAB, RBC, and RAC.
6. Now connect A and D together with an alligator clip—it is very important
that the connection is good—and find the resistance from A (or D) and B
(or C). Call this Rparallel.
Part 2—Measuring currents through a coil
1. To measure current, you should use the 20A connector and setting on the
multimeter (acting now as an ammeter). Keep the other connector in
“com”.
2. It is important to “break the circuit” and then reconnect through the
ammeter. This is easy to forget and student often try to measure current
just like they would measure voltage. That would be wrong.
3. Measure the current by putting the battery pack across all of the loops.
Then you should try to see what happens if the current goes through only
two and then only one loop. Call these currents I1, I2, and I3. AT THE SAME
TIME you should use another multimeter as a voltmeter to check on the
voltage of the battery pack.
Analyze your data
What does “analyze” mean? You have a set of measurements of voltages,
currents, and resistance. How do they relate to one another? To what extent do
they fit your expectations? To what extent are they different? Clearly explain
your reasoning.