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A Different Perspective – Lenz’s Law!

By Jaisen Leung in HSC
8th of April 2021

Faraday’s law and Lenz’s law are often seen as two separate laws. However, this article will delve into how Lenz’s law is really just an extension upon Faraday’s law and how you can show the marker just that!

Faraday’s law states that a conductor will induce an EMF if it experiences a change in magnetic flux. Lenz’s law on the other hand states that the induced current must flow such that it creates a magnetic field that opposes the change in flux.

While similar, the 2 key differences lie in the fact that:

1) Lenz’s law requires a closed circuit given that it requires a current to be formed. This is unlike Faraday’s law whereby the circuit does not need to be closed as only an EMF is induced.

2) This current will create a magnetic field to oppose the change in flux (hence the negative in the formula ). Faraday’s law does not indicate the direction of the induced EMF.

Understanding that the two laws are related, yet different is one thing. Showing that to the marker is another! When answering questions, you should incorporate both laws in your answer to show the marker that you are aware of the distinctions between the two. Let’s have a look at an example to demonstrate how this can be done.

HSC 2018, Question 22

 

SAMPLE ANSWER

As the magnet spins, the metal disc experiences a change in flux, inducing an EMF in the metal disc (Faraday’s law), creating a current that produces a B-field to oppose the change in flux (Lenz’s law).

This causes the metal disk to spin with the magnet to remove the relative motion between the two.

First off, I want to note that this is exactly how I format my answers and have not shortened my answer for this article. I like to use dot points as it keeps my answers clear and concise (I promise it’s allowed). Next, I want to note that the underlined words can be used for practically any Lenz’s law question! Regarding my answer, I’d like you guys pay attention to the first dot point specifically, demonstrating how I’ve incorporated both laws in the same sentence to show the marker I understand both their relationship and distinctions. As such, the marker can tell that you truly understand your content as opposed to having just memorised it!

I hope that this article has now either helped you gain a deeper understanding about these fundamental laws, or helped solidify your knowledge of what you already know 🙂

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