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Physics students are most likely to be familiar with Lenz's Law. You may have been asked to calculate the direction of the current induced in a given loop using Lenz's Law. The Lenz’s La states the following:

‘An induced electromotive force generates a current that induces a counter magnetic field that opposes the magnetic field generating the current.’

In other words, Lenz's Law is based on the principle of Newton’s Third Law of Motion and conservation of energy. Here is a complete overview of this topic. Whether you need to understand the basics of this topic or find answers to questions, the following information might help you.

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What is Lenz's Law?

According to Lenz’s law of electromagnetic induction, a changing magnetic field induces the direction of the current in a conductor. This induced current creates a magnetic field that opposes the magnetic field that produced it in the first place. Fleming’s right-hand rule gives you the direction of this current flow. Contact the experts of Essayassignmenthelp.com.au to get the best guidance on the Code of Lenz Law.

Let’s break it down for your better understanding.

  • Let’s say a magnetic field induced a current. So, this induced current will create its own magnetic field as well.
  • The latter will always oppose the magnetic field that produced it.

Lenz’s law is named after Emil Lenz and is one of the most convenient methods for calculating the direction of the induced current. It is also based on Faraday’s law of induction. According to Faraday, a changing magnetic field induces a current in the conductor.

Lenz's law, on the other hand, states that the direction of the induced current opposes the initial magnetic field. The change in the magnetic field may happen because of a magnet moving away from or towards the coil.

Lenz's Law Formula

The formula of Lenz’s Law:

e.m.f.=−N(ΔΦ/Δt)

emf is the induced voltage which is also known as electromotive force

  • N indicates the number of loops
  • ΔΦ indicates the change in magnetic flux
  • Δt indicates the change in time

The negative sign shows the polarity of the induced EMF. It also indicates that the change in magnetic flux and the induced EMF consist of opposite signs.

You may find the resemblance between Lenz’s Law in Faraday’s Law as well.

Faraday's law helps in the prediction of how a magnetic field interacts with an electrical circuit to generate an electromotive force or EMF. The formula is:

ΔΦB/∆t (through a fixed area) = -Σaround loop E∙r (at a fixed time)

The minus sign conveys the direction of the circulation.

As mentioned earlier, Lenz’s law is based on the principle of conservation of energy. Lenz’s law exists because of the law of conservation of energy. Imagine a scenario where the law of conservation of energy never existed.

In that case, the magnetic field created by the induced current flows in the same direction as the initial field. Then the two magnetic fields would join and become a larger magnetic field. This larger magnetic field induces another current within the conductor, which is most likely to be twice the magnitude of the original induced current.

It will be a never-ending process. Thus, it must obey the law of conservation of energy.

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Lenz's Law Example

Here are a few examples of Lenz’s Law to help you understand the topic even better:

In a large aluminum or copper pipe, large magnetic fields cause counter-rotating currents. If you drop the magnet through the pipe, you will be able to experience this phenomenon. As the magnet drops down the pipe, it descends at a lower rate than what it was dropped at. Thus, you can use the right-hand rule to determine the direction of the induced current.

The moving of a coil of wire into or out of a magnetic field is also a classic example of Lenz’s Law. The magnetic flux through the loop increases as the loop moves into the field. This movement also induces an opposing current to the rate of change of flux. Thus, it causes a magnetic field that flows in the direction of the motion. Now let’s say the coil is moving towards you. Thus, according to Lenz's Law and the right-hand rule, the current flows in the counter-clockwise direction. 

Lenz's Law Applications

Here are the common applications of Lenz’s Law:

  • The most common application of Lenz’s Law is in storing magnetic energy in an inductor. A current is induced when a source of emf and an inductor are connected. The back emf uses the inductor to oppose this increase in current. Now the external source of emf needs to do some work to establish the flow of current eventually. This work is done by the emf stored in an inductor. You can recover this emf after removing the external source of emf from the circuit.
  • You can also find its application in electric generators. The generator induces a current whose direction opposes and causes rotation of the generator. The generator eventually needs more mechanical energy.
  • Lenz's law also finds application in electromagnetic braking and induction cooktops.

Where is Lenz's Law Used?

You must have an idea about where this law might be used by now after reading the above-mentioned applications. Lenz's law lets you determine the direction of the emf induced by a changing magnetic field using a coil or loop of wire. It provides us with the direction and magnitude of the electric current induced due to the change in magnetic flux in the coil. All in all, we use Lenz’s law when we have to determine the direction of the induced electric current. Here are other areas where it can be used:

  • Electromagnetic brakes
  • Induction cooktops
  • Eddy Current Balances
  • Eddy current dynamometers
  • Card readers
  • Metal detectors
  • The braking system on trains
  • Microphones

Lenz's Law Experiment

You can try out the following experiments to find out the direction of the emf induced and current.

First experiment

  • The current in the coil flows in the circuit.
  • The magnetic lines are formed.
  • The magnetic flux increases.
  • So, the direction of the flow of induced current opposes the increase in magnetic flux.

Second experiment

The coil carrying around current is wound around an iron rod where its left end behaves like the N-pole. The induced current forms as it moves towards the coil.

Third experiment

The coil is pulled towards the magnetic flux and the area of the coil that is inside the magnetic field decreases.

According to Lenz’s law, when the induced current is applied in the same direction, it opposes the motion of the coil. The magnet exerts the force in the loop to produce current.

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FAQs

  1. How is Lenz's Law connected to Conversation of Energy?

According to the law of conservation of energy, you can neither create nor destroy energy. You can only change it from one form to another. As per Lenz's law, the direction of the induced current opposes the change in magnetic flux. Thus, it requires an extra effort to work against opposing forces. This extra effort is converted into electrical energy, which proves the law of conservation of energy.

  1. Difference Between Lenz's Law and Faraday's Law

There is a slight reflection of Lenz’s law in Faraday's Law, where the negative sign indicates the opposing direction of electric current. But, they are different. Faraday’s law helps in the determination of the magnitude of the emf produced. Lenz’s law, on the other hand, lets us know about the direction in which the current will flow.

  1. What is the Importance of Lenz's Law?

Lenz’s law helps in the determination of the direction and magnitude of the electric current induced due to the change in magnetic flux in the coil on the conductor. This law governs the functioning of appliances such as Electromagnetic brakes, Induction cooktops, Eddy Current Balances and more.

  1. How Does Lenz's Law Determine Direction?

According to Lenz’s law, the direction of the induced magnetic field is opposite to the initial field that produced it. That means if you know this direction, you can determine the direction of the induced current using Fleming’s right-hand rule, where you point your thumb in the direction of the magnetic field.

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