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Lenz's Law

An electric current always creates a force opposing the force inducing it.

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Don't Forget Your Coat!

Credit: lululemon athletica
License: CC BY-NC 3.0

A Winter Coat [Figure1]


Lenz's Law states that an induced electromotive force generates a current that induces a counter magnetic field that opposes the field generating the current.

Lenz's Law

Just like you, nature often resists change. When you’re inside, you may just be wearing a t-shirt and shorts. But when you’re about to leave the house, and it is cold outside, you’d probably want to put on a sweatshirt. And if you’re going back inside, you may take off your sweatshirt. However, when your surroundings aren’t changing, it is unlikely that you’d change clothes.

A coil passing over an electric field works in the same way. When it crosses over the field, it induces a current in such a way that an electric field opposite to the one its crossing is created, thus neutralizing the field. You can find the direction of the current for this to happen using the right hand rule, as well as the force being created. When the coil moves back off the field, another current is induced to bring it back to normal. However when the coil is just passing over a constant field, it won’t create a new current.

Creative Applications

1. If you are going outside, and it is cold outside, are you going to put on something that will make you cold, or something that’ll make you hot?

2. If a neutral coil passes over an electric field moving out of the paper, will the induced field be moving into the paper or out of the paper? Will the current that creates this field spin clockwise or counterwise?

3. You can heat a pan on an induction cooktop, which provides no heat. Underneath the cooktop there are coils that can create changing magnetic fields. Use Lenz's Law to explain how these coils can give energy to the pan.

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  1. [1]^ Credit: lululemon athletica; License: CC BY-NC 3.0

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