[SND] exp26.rm               


This demonstration literally shows the Faraday’s law  dF\dt = -e (t) where F(t) is the magnetic flux and e (t) is the induced voltage.


What you  need:

1)      Two coils, one with ca 500 windings, one with ca 1000 windings. These numbers

are not all that important. They are the ones I used and they gave good results.

The main thing is that it should be a rather big difference in the number of windings.

2)      A two-channel oscilloscope.

3)      An iron bar long enough to stick through both coils simultaneously.


4)      Cables and plugs

5)      A signal-generator





What to do:

1)      You connect the signal-generator to the biggest coil .

2)      This coil you also connect to one of the channels on this scope.

3)      The smaller coil you connect to the other scope-channel

4)      Place the smaller coil onto of the biggest one and place the iron bar inside both coils.

5)      Send a triangular low voltage through the big coil and adjust the scope-settings so you get a clear signal on this channel.

6)      Then adjust the settings for the other channel.

7)      Hopefully you will now have a rectangular voltage on this channel. (Most likely it will be somewhat fuzzy, but hey we did it…..)

8)      If you change your input-signal to a sine-form, your output will be a cosine-form.





Why it happens:

The ac-voltage in the big coil induces a variable magnetic field through both coils.

This mag.field will be in phase with the ac-voltage.

The variable magnetic field in turn induces an ac-voltage in the second coil, which will be 180 deg out of phase with the mag field because of Faradays law.

In other words, the signal-curve from the small coil will be the negative time-derivative of the signal-curve fed to the big coil.