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Lenz's Law

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Here's a little exercise in magnetic induction. We're going to use a coil of wire and a cylindrical magnet and we're going to induce a current in the coil by putting the magnet into the coil. And to see whether or not there's a current, we're going to connect the coil up to this very sensitive meter, which reads in microamperes. First thing I want to do is find out which is the north pole of my cylindrical magnet, so I use a compass for that. I can verify that the red end of the compass needle is pointing to the north. And now I'll bring in the end of my bar magnet that is taped and you can see that what its doing to the compass. If I turn the magnet around, you can see what happens so that should be enough information for you to figure out weather the taped end of the magnet is north pole or south pole okay back to the coil. I need to connect my coil up to the ammeter first thing you want to note how the wire is wrapped around this here's the end of the coil which is labeled red that's just so you can keep track of which end is which and you can see how the wire wraps around that. Okay, I'm going to take this end and clip it to the positive side of my ammeter and take the other end and clip it to the negative side of my ammeter. There is no battery in this circuit we're going to produce a current using the effect of magnetic induction only. Alright now we won't see a big effect in the needle so keep your eye on it. And what you want to see is which way it deflects initially if it deflects this way its positive current if it deflects this way its negative current, no deflection no current. Okay I'm going to take the taped end of the bar magnet push into the red end of the coil; here goes, and I'll pull the magnet out opposite effect. And just to be complete about it let's use the other pole of the cylindrical magnet, push it in to the red end of the coil hold it there for a moment, pull it back out. with that information you'll do some checking to determine whether Lenz's law is consistent with these results.


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