2) Sketch several turns of the coil on the cylinder below. The red side of the spool is labeled R.
3) Check your bar magnet with a compass (check the compass first!) to make sure you know which pole is really N. Connect the positive lead of the multimeter to the outer end of the coil and the negative lead to the inner end. You'll probably have to hold the leads in place.
4) Now you're going to push the magnet into the coil. You'll push the N pole into the red end of the coil as shown in the diagram. Get ready to read the meter. When you push the magnet into the coil, you'll get a small change in the reading. You don't have to record the number but be ready to note whether the reading goes positive or negative. Now push the magnet in quickly and stop. Record in the table on the back whether the reading was positive or negative.
5) Now you need to determine the direction of the induced current in the coil. Note that a positive meter reading means that conventional current in the circuit goes into the positive terminal of the meter and out of the negative terminal. Show the direction of the induced current on your coil diagram.
6) Given the direction of the induced current, determine where the N pole of the coil's induced field is located. Label this pole on your diagram. (Which way do the field lines point inside the coil?)
7) Now do the following tests, each time determining whether the meter reading goes positive or negative and which end of the coil (left or right) is the N pole of the induced field. Record all results in your lab book in a table patterned after the one below.
a) With the magnet inside the coil, pull the magnet out quickly with the N pole coming out last at the red end.
b) Now push the S pole in quickly at the red end.
c) Finally, pull the magnet out (quickly, of course) with the S pole coming out last from the red end.
| Action | Sign of current (+/-) | Location of N pole
of coil (red/white) |
| N pole pushed in | ---------------------- | ---------------------- |
| N pole pulled out last | ---------------------- | ---------------------- |
| S pole pushed in | ---------------------- | ---------------------- |
| S pole pulled out last | ---------------------- | ---------------------- |
9) Now it's time to see if Lenz' Law is consistent with your results. For the two cases where the magnet is pushed into the coil, do your results agree with Lenz' Law? Explain.
10) For the two cases where the magnet is pulled out of the coil, do your results agree with Lenz'
law? Explain.
11) If any of your results were unexpected, perhaps you need to take a closer look at Lenz' Law.
Just what is it that the induced field opposes
