Hey Ray: Lenz's Law


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Jan 04, 2024

Hey Ray: Lenz's Law

By Ray Petelin February 18, 2023 / 9:28 AM

By Ray Petelin

February 18, 2023 / 9:28 AM / CBS Pittsburgh

PITTSBURGH (KDKA) - Not all metals are magnetic, but non-magnetic metals can interact with magnets in very interesting ways.

Two of the metals we will work with for our experiment are copper and aluminum. Neither are magnetic. We are also going to be using rare earth magnets, also known as neodymium magnets. These very strong magnets can be dangerous and do pose a pinching hazard, so make sure a responsible adult supervises this activity.

I will also say that viewing the video posted with this article will help you see the demonstrations described here.

Even though the copper is not magnetic, we can see that the magnets do interact with it, but for that interaction to happen, the magnets need to be in motion!

You can see in the video that accompanies this article, how slowly the magnets slide down the bar of copper. If you were to try to slide the magnet across the copper, you can also feel the resistance of that interaction occurs.

Now with the aluminum can, we can show this interaction in a different way. If we wave the magnets over the can quickly, the can begins to move. Even though the aluminum can isn't magnetic, there is still something happening.

This is a known interaction that leads us to an even cooler experiment that demonstrates Lenz's Law.

Lenz's Law states that the magnetic field of any induced current opposes the change that induces that field. This is something that is easier to show first. We are going to drop our powerful, rare earth magnets through a roll of aluminum foil.

The same stuff in your kitchen drawer. Remember, aluminum is not magnetic, but we already showed you that moving magnets and some metals do have a relationship.

As the magnets fall through the tube, they slow down!

If you think they are slowly sliding through the tube because the magnets are rubbing, we want to show you a view through the tube, where the magnets are not even touching the sides!

This is Lenz's law in action!

If you have ever put the like-sided poles of two magnets together, you would get the magnets to repel, or push away from each other. That is sort of the scenario we are creating here.

As the magnet falls through the foil tube, the magnetic field changes. This creates an electric current. That current creates its own magnetic field, and that electromagnetic field works against the change that produced it.

It is a fancy way of saying the falling magnet works against itself, causing it to fall slowly.

Too bad our refrigerator is magnetic because Elizabeth wants to hang up the portraits she drew of me!

Meteorologist Ray Petelin joined the KDKA Weather Team in October 2018, but is no stranger to the weather in Pittsburgh and Western Pennsylvania. He has been forecasting in Pittsburgh since 2011 and in Western PA since January of 2003.

First published on February 18, 2023 / 9:28 AM

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