Lenz’s Law

What is Lenz’s Law?

A Russian physicist Heinrich Friedrich Emil Lenz introduced his law regarding the determination of the direction of an induced electric current in a magnetic field in 1834. This law is known as Lenz’s law.

According to Lenz’s law an induced current in a magnetic field will flow in a direction such that it opposes any occurring change in the magnetic field. Len’s law derives its basis from the principle of conservation of energy and Newton’s third law in classical mechanics. Lenz’s law is the easiest way to determine the direction of an induced current in the magnetic field. 

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Lenz’s Law formula:

Lenz’s law has the basic of Faraday’s law of electromagnetic induction as according to the Faraday’s law of electromagnetic induction a changing magnetic field will induce a flow of current within an electric conductor while in Lenz’s law it is said that the induced current direction which opposes any change in the magnetic field which generated it.

Therefore,the formula of Lenz’s law is written just as the formula of Faraday’s law, however with a negative sign.

                       Emf(ϵ) = −N(∆Φ/∆t)

Here, Emf = electromotive force

          N = The number of loops 

         Δϕ = Change within the magnetic flux

          Δt = Change within time.

How to bring change in the magnetic field?

We can bring change in the magnetic field intensity in a closed loop via different ways. Let us discuss some of them below :

• A change in the magnetic flux can be brought by rotating the coil which is relative to the magnet

• A change in the magnetic flux can also be brought by moving the coil into the magnetic field

• Bringing the coil out of the magnetic field can also bring a change in the magnetic flux

• We can also change the area of the coil which is placed in the magnetic field

• We can move the magnet towards the coil to bring a change in the magnetic flux

• Moving the magnet away from the coil can also bring change in the magnetic flux dt

Lenz’s Law experiments:

Lenz’s law is used to determine the direction of an induced current and electromotive force (emf) in a magnetic field. He himself conducted some experiments to prove his theory. Here we discuss his three experiments below:

First Experiment :

Lenz conducted his first experiment and he concluded that when a current in a coil is induced or as a current starts flowing in a coil, the magnetic field lines will increase and the direction of the flow of the induced current will oppose the increase in the magnetic flux.

Second Experiment:

Lenz conducted his second experiment by binding a current carrying coil on an iron rod with its left end behaving as the north pole(N) and then it is moved towards the coil S and then an induced current will be produced there.

Third Experiment:

Lenz conducted his third experiment in which he pulled the coil towards the magnetic flux then the coil linked to it kept on increasing. This continuous decay in the coil shows that the area of the coil inside the magnetic field is decreasing. 

So if we analyze Lenz’s theory we conclude that the flow of the coil is opposed when the induced current is applied in the same direction. For the purpose of generating current force is exerted by the magnet in the loop and for the purpose of opposing the change a force must be exerted by the current on the magnet. 

Applications of Lenz’s Laws:

Many modern electrical and non-electrical gadgets work on Lenz’s principles of opposition. Let us discuss some of them:

• Lenz’s law is used in the operation of electromagnetic brakes

• Induction cooktops, which is an electric stove used for cooking, works on Lenz’s law

• Lenz’s law is applied in electric generators

• Lenz’s law is used to balance eddy currents

• Lenz’s law is used in card readers, microphones, metal detectors etc

• The braking systems on trains also work according to Lenz’s law

• Eddy current’s dynamometer works on Lenz’s law

Conclusion 

Thus, after analyzing Lenz’s law of electromagnetism we can say that if we connect a source of an electromagnetic field across an inductor the current will start following through it. The electromagnetic field will resist any change and increase or decrease in current through the inductor. In Lenz’s law an induced current in a magnetic field will flow in a direction such that it opposes any occurring change in the magnetic field. The formula of Lenz’s law is written just like the formula of Faraday’s law however, with a negative sign in it. It derives its basics from the principle of the conversion of energy and Newton’s third law of motion according to which for every action there is an equal opposite reaction. If a magnetic field is created by an induced current which is equal and opposite to the direction of the magnetic field that has created it, only it can oppose the change in the magnetic field in the area. Not only this, Lenz’s law also upholds the principle of the conservation of energy. If the current is induced in the opposite direction, there will be an immediate action by drawing the bar magnet into the coilin addition to the heating effect which will be a violation of the principle of the conservation of energy.

As Lenz’s law tells about the direction of the induced current in a conductor loop, it is a qualitative law however it does not say anything about its magnitude.