lenz law experiment

• Electrostatics

Named after Emil Lenz, Lenz’s law depends on the principle of conservation of energy and Newton’s third law. It is the most convenient method to determine the direction of the induced current.

What is Lenz’s Law?

Lenz’s law states that

The induced electromotive force with different polarities induces a current whose magnetic field opposes the change in magnetic flux through the loop in order to ensure that the original flux is maintained through the loop when current flows in it.

Named after Emil Lenz, Lenz’s law depends on the principle of conservation of energy and Newton’s third law . It is the most convenient method to determine the direction of the induced current. It states that the direction of an induced current is always such as to oppose the change in the circuit or the magnetic field that produces it.

Lenz’s Law Formula

Lenz’s Law is reflected in the formula of Faraday’s law . Here the negative sign is contributed by Lenz’s law. The expression is –

Emf is the induced voltage (also known as electromotive force).

N is the number of loops.

Following is the table with links to other Physics-related laws:

Lenz’s Law Applications

Lenz’s law applications are plenty. Some of them are listed below-

• Eddy current balances
• Metal detectors
• Eddy current dynamometers
• Braking systems on train
• AC generators
• Card readers
• Microphones

Lenz’s Law Experiment

To find the direction of the induced electromotive force and current we look to Lenz’s law. Lenz proved some experiments in accordance with his theory.

First Experiment

In the first experiment, he concluded that when the current in the coil flows in the circuit, the magnetic field lines are produced. As the current flow through the coil increases, the magnetic flux will increase. The direction of the flow of induced current would be such that it opposes the increase in magnetic flux.

Second Experiment

In the second experiment, he concluded that when the current-carrying coil is wound on an iron rod with its left end behaving as N-pole and is moved towards coil S, an induced current will be produced.

Third Experiment

In the third experiment, he concluded that when the coil is pulled towards the magnetic flux, the coil linked with it decreases, which means that the area of the coil inside the magnetic field decreases. According to Lenz’s law, the motion of the coil is opposed when the induced current is applied in the same direction.

To produce the current, force is exerted by the magnet in the loop. To oppose the change, the current on the magnet must exert a force on the magnet.

Frequently Asked Questions – FAQs

How is lenz’s law conservation of energy, what is the difference between lenz’s law and faraday’s law.

Lenz’s law is about the conservation of energy applied to the electromagnetic induction, whereas Faraday’s law is about the electromagnetic force produced.

What is the prime importance of Lenz’s law?

What does the negative sign indicate in lenz’s law.

The negative sign in Lenz’s law indicates that the induced emf in the coil is in the opposite direction of the magnetic flux, which is linked with the coil.

Where is Lenz’s law used?

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What is Lenz’s Law : Formula, Significance & Its Applications

An efficient method for generating electricity is known as electromagnetic induction . From electricity generation to distribution, it is used everywhere. This is a procedure where a Voltage or electromotive force is generated across a conductor through changing Magnetic Flux or Magnetic Fields. This electromagnetic induction theory was based on Faraday’s laws & Lenz’s law which were discovered in the year 1830 by Michael Faraday.

The Electromagnetic Induction generation can be achieved through two methods where in the first method an electrical conductor is located within a moving magnetic field and in the second method the electrical conductor is moving steadily in a fixed magnetic field. So, this article discusses an overview of Lenz’s Law with its examples.

What is Lenz’s Law?

The name Lenz’s Law was taken from the physicist Emil Lenz when he invented this law in the year 1834. Lenz’s law states that; the flow of current direction which is induced in a conductor through a varying magnetic field then the magnetic field formed through the induced current will resist the early changing magnetic field.

Once a current is induced through a magnetic field, then the magnetic field generated through the induced current will form its magnetic field. So, this field will be restricted through the magnetic field that formed it.

Lenz’s law mainly depends on Faraday’s law of electromagnetic Induction because Faraday’s law states that a varying magnetic field will induce a flow of current within an electric conductor while Lenz’s law states that the induced current direction which restricts the early changing magnetic field which generated it. Thus, this is denoted in Faraday’s law formula through the negative sign.

ϵ = −dΦB/dt

The magnetic field can be adjusted by changing its field’s strength or by moving the magnet in the coil direction or moving away from the coil, etc. Thus, we can say that the electromagnetic field’s magnitude which is induced within the circuit is proportional to the change rate of flux.

Lenz’s Law Formula

According to Faraday’s Law, when an emf is produced through a change within magnetic flux is known as Lenz’s law. Here, an induced current can be generated through the induced EMF’s polarity where the magnetic field restricts the primary changing magnetic field. In Faraday’s law of electromagnetic induction, the negative sign mainly specifies the induced EMF or ε & the change within magnetic flux or δΦB has reverse signs. Here, Lenz’s law formula is shown below:

Lenz’s Law Formula Emf = -N (ΔΦ/ Δt)

‘Emf’ = Induced voltage or electromotive force.

‘N’ = The number of loops.

‘Δϕ’ = Change within magnetic flux.

‘Δt’ = Change within time.

Lenz’s Law & Conservation of Energy

The induced current direction through Lenz’s law must generate a magnetic field to obey the energy conservation that restricts the magnetic field that produced it. This law is an outcome of the energy conservation law.

Once the magnetic field formed through the current induced will be in a similar direction like the field generated it, after that these magnetic fields would merge to make a bigger magnetic field.

This magnetic field will induce one more current in the conductor to twice the induced current’s magnitude. Thus, we can conclude that if Lenz’s law did not state that the induced current should form a magnetic field to restrict the created field, then we would finish up with a nonstop positive feedback loop for breaking the protection of energy.

This law generally obeys Newton’s 3rd law of motion, which states that for each action there is always an equivalent and reverse reaction. If the induced current forms a magnetic field that is equivalent and reverse to the magnetic field’s direction that makes it, then only it resists the magnetic field change within the region.

This Lenz’s law experiment is mainly for discovering the induced electromotive force direction & current we look for Lenz’s law. For this law, the following three experiments were proved through his theory.

1st Experiment

In this experiment, Emil Lenz said that when the current flows within the coil of the circuit then generate magnetic field lines. When the current supply within the coil increases, the magnetic flux will be increased. So, the induced current flow direction will restrict once the magnetic flux enhances.

2nd Experiment

In this 2nd experiment, Lenz declared that once the current-carrying coil is wounded over an iron rod using his left end which acts like an N-pole & is turned toward the ‘S’ coil, then an induced current will be generated.

3rd Experiment

In this 3rd experiment, Lenz stated that once the coil is dragged in the direction of the magnetic flux, then the coil which is associated through it decreases. So, based on Lenz’s law, the coil’s motion is restricted once the induced current is provided within a similar direction.

To generate an induced current, the magnetic field uses a force over the coil, and in sequence, a force is used through the current supply on the magnetic field to restrict it.

Lenz’s Law Problems and Solutions

1). A circular shape wire coil including 350 turns & a 7.5 cm radius is located horizontally over a table. A consistent magnetic field positioning openly up is gradually switched on, so the magnetic field strength can be expressed like a time function as B(t) = 0.02(T /s2) ×t2. So, what is the complete EMF within the coil like a function of time, and in which way does the current supply?

EMF = (-N) x (22/7 x r^2) x (d/dt B)

= -350 x 22/7 x (0.075 m)^2 x 2 x 0.020 T x t

= -25 t * (Tm^2/ s^2)

= -25 t V/s

In clockwise direction it supplies.

2). If the flow of current within a wire is from B to A direction then find out the induced current direction within the metallic loop wire kept aside as shown in the following figure.

Based on Lenz’s law, the induced current direction will restrict the cause of its production. Thus, the current flow within a loop will induce to support the flow of current within the wire which means in a similar direction. As a result, the current direction within the loop will be in a clockwise direction.

3). In a circular loop, resistance ‘R’ and area ‘A’ turns through an angular velocity ‘ω’ on an axis throughout its diameter is shown below. The loop’s plane is primarily perpendicular to a stable magnetic field ‘B’. Please find the induced current within the circle loop.

The direct magnetic flux throughout the loop is

ΦB = BA cos θ

Here, θ = ωt, thus, ΦB = BA cos ωt

According to Faraday’s law,

ϵ = −dΦB/dt = – ϵ = −d/dt [BA cosωt]

ϵ = [BAω sinωt]

The current induced can be expressed as

I = E/R = (BAω/R) sinωt

Here, both the current & the induced emf change sinusoidally. So, the emf amplitude is ‘BAω’ & the current is BAω/R.

The significance of Lenz’s law includes the following.

• Lenz’s law tells us two main things regarding how the magnetic field changing will interact with a conductor loop.
• This law depends on energy conservation but not on the momentum conservation
• This law is available to rule how magnetic fields are generated through conductors carrying AC or DC.
• This law states an induced current’s direction to the rate of change within the inducing magnetic field.
• In electromagnetism, this law is a very significant concept

Limitations of Lenz’s Law

The limitations of Lenz’s Law include the following.

Once a magnet is moved in the direction of the coil, then the exterior magnet field will induce a current within the coil to make its inside magnet field through a similar magnitude however with the reverse direction, hence opposing the change.

Once the magnet moves through the coil or other face of the coil, then the flow of current will change the direction & the inside magnetic field will be enhanced within a similar direction due to the external magnetic field, so again opposing the change.

Where is Lenz’s law used/Applications?

The applications of Lenz’s law include the following.

• This law is very helpful in understanding the stored magnetic energy concept within an inductor
• Whenever an emf source is connected across an inductor, then-current starts flowing through it, and back emf will restrict the increasing flow of current throughout the inductor. To create the current flow, the exterior emf source has to do some work to conquer this opposition. So this work can be done through the stored emf within the inductor & it can be improved once the external source of emf is detached from the circuit.
• Lenz’s law specifies that the induced emf & the change within flux have reverse signs which give a physical understanding of the alternative of a sign within Faraday’s law of electromagnetic induction.
• This law applies to electric generators. Once the flow of current is induced within a generator, the then induced current direction will oppose & makes the generator rotate. Thus, the generator needs more mechanical energy to provide back emf while using an electric motor .
• It is used in induction cooktops & electromagnetic braking.
• It is used in AC generators & electric generators
• Used in metal detectors
• Eddy current dynamometers
• Used in braking systems of train
• Microphones
• Card Readers

1). How Lenz Law is a Consequence of Conservation of Energy?

Lenz’s law mainly depends on the concept of energy conservation. We know that in Lenz law the current induced is frequently tends to restrict the source which generates it. Thus, to do work against opposing forces we need to put some additional effort. So this additional work is direct to periodic change within magnetic flux so a huge current will be induced. Therefore, the additional effort is simply changed into electrical energy which is conservation of energy law.

2). What is Lenz law Igcse?

The Igcse board stands for “International General Certificate of Education” and this law from this board states that the current which is induced is always supplied in such a way that to oppose the motion or charge generating it.

3). What happens if Lenz law is reversed?

If Lenz’s law is simply reversed then the induced current generates flux in a similar direction like the original change. So this high change within the flux can generate an even larger current, followed through a still bigger change within flux. The flow of current will continue to rise indefinitely for generating power even after the creative stimulus is finished.

4). What is the prime importance of Lenz’s law?

This law is mainly used for determining the induced current’s direction

5). What does the negative sign indicate in Lenz’s law?

In Lenz’s law, the negative sign mainly specifies that the emf induced within the coil is in the reverse direction of the magnetic flux. Here this flux is connected through the coil.

Thus, this is all about an overview of Lenz’s Law discovered by Friedrich Emil Lenz. This law mainly depends on the conservation of energy principle & also Newton’s third law. So, it is the most suitable technique to conclude the induced current direction. He also discovered that the magnetic field’s strength is proportional to the power of the magnetic induction. Here is a question for you, what is Faraday’s Law of electromagnetic induction?

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Lenz's Law

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• Kaustubh Miglani
• Josh Silverman

Lenz's law states that whenever there is a change in the magnetic flux through a conducting loop, a current arises to produce a magnetic field that balances the change, i.e. to keep \(\int_A \vec{B}\cdot \vec{n}\) constant. This is a result of Faraday's law of induction .

An externally applied magnetic field through an area induces a current. The induced magnetic field due to the induced current opposes the external field by Lenz's law.

Lenz's Law and Faraday's Law of Induction

Experiment demonstrating lenz's law.

When a magnetic field \(\vec{B}\) goes through a closed conducting loop of area \(A\), it causes a magnetic flux: \[\Phi_B = \vec{B} \cdot \vec{A}\] Here \(\vec{A}\) is the unit vector that points orthogonal to the surface enclosed by the loop everywhere. The dot product above means that a magnetic field at an angle to the loop has less magnetic flux through that loop than if it were orthogonal to the plane of the loop. Formally, if the loop does not lie in a plane, the flux is written as an integral over the surface enclosed by the loop: \[\Phi_B = \int \vec{B} \cdot d\vec{A}\]

If the loop is instead a solenoid or other coil with many turns, each turn of the coil is usually approximated by its circular cross-section and the flux is summed over every turn.

Faraday's law of induction states that when the magnetic flux through a closed conducting loop changes in time, an emf is induced in that loop: \[\varepsilon_{\text{induced}} = -\frac{d\Phi_B}{dt}.\]

Since the loop is conducting, it has some resistance \(R\), and the emf induces a current according to Ohm's law : \[I_{\text{induced}} = \frac{\varepsilon_{\text{induced}}}{R} = -\frac{1}{R} \frac{d\Phi_B}{dt}.\]

In turn, the induced current causes a magnetic field according to Ampere's Law , which itself has a flux through the closed loop. According to Lenz's law, the direction of the induced current and resultantly the induced magnetic flux opposes the original magnetic flux. It is important to note that the direction of the change in flux may be opposite to the direction of the field, for instance, if the strength of the field is decreasing or the field is tilting.

Since the sign of the induced current determines the direction of the induced magnetic flux, the negative sign in Faraday's law is also often referred to as Lenz's law rather than the conceptual statement.

Lenz's law is what allows inductors in circuits to function. Inductors have a large voltage across them when the current is changing rapidly in the circuit. This is because inductors are often solenoids or toroids in which current causes a magnetic flux. When the current changes rapidly, the magnetic flux changes rapidly, and a large emf is induced that opposes the original change in current.

Explain how a simple electric motor works using Lenz's law. Solution: As a simple motor, consider a coil of wire that is stationary in a vertical magnetic field such that there is no magnetic flux through the coil: A coil of wire in a vertical magnetic field. The area vector \(\vec{A}\) for the plane of the wire is perpendicular to the field, so there is no magnetic flux. If the coil is rotated slightly, the angle between the area vector and the magnetic field is no longer zero. Therefore, the magnetic flux increases in time. By Faraday's law of induction, this induces an emf that causes a current in the coil. This induced current produces a magnetic field that opposes the applied field, since the flux of the applied field is increasing: As the coil tilts, the area vector \(\vec{A}\) is no longer perpendicular to the applied magnetic field \(\vec{B}\), so the magnetic flux of the applied field increases. This induces an emf and thus a current in the coil which results in an induced magnetic field opposing the applied field. Recall now that like poles of permanent magnets repel and opposite poles of permanent magnets attract. The reason is derived from the fact that opposite poles have parallel field lines, while like poles have antiparallel field lines. Here, the vertical component of the induced magnetic field from the coil points antiparallel to the applied field, acting as a "like pole." This causes the applied field to push down on the coil, repelling the induced field and causing the coil to spin (provided that the field is weaker on one side of the coil than the other). Once the coil flips halfway over, the magnetic flux will begin to decrease and the force on the coil will act in the opposite direction To counteract this, one side of the coil is typically covered with insulating material that reduces the amount of current flowing through the coil. As a result, by initially changing the angle of the coil quickly, a very large emf and a large induced magnetic field can be created from the coil that causes the coil to rotate quickly enough to complete a full revolution. The cycle then begins again, driving the coil through another full revolution and so on.

A wire loop in the \(x\)-\(y\) plane sits in an external uniform magnetic field oriented at 30 degrees from the positive \(z\) direction in the \(x\)-\(z\) plane, which increases in strength over time. In which direction does the induced magnetic field at the center of the wire loop point in the \(x\)-\(z\) plane?

A mass \(M\) pulls the conducting bar through a vertically oriented magnetic field.

In the above picture, a mass \(M\) falls under the influence of gravity, pulling with it a conducting bar of mass \(m\), resistance \(R\), and length \(\ell\) that sits on a U-shaped piece of metal in a vertically oriented magnetic field perpendicular to the plane of the U, pointing in the positive-z direction. In which direction does the induced current flow?

A common experiment demonstrating Lenz's law is the "magnet drop" experiment. In this experiment, a(n often powerful, neodymium) magnet is dropped through a conducting tube, often made of copper. The changing magnetic flux as the magnet falls induces a current in the tube which creates a magnetic field opposing the magnetic field of the permanent magnet. Because like poles of a magnet repel and the induced magnetic field appears to be a like pole at either end of the magnet, a magnetic force is exerted on the permanent magnet that slows its fall due to gravity.

A powerful magnet dropped in a copper tube made to levitate in the tube via Lenz's law; here the short copper tube is rotated repeatedly to keep the magnet suspended [2].

A permanent magnet of mass \(M\) is released from rest at the middle of a long copper tube of resistance \(R\) and cross-sectional area \(A\) as above. Make the approximation that the strength of the magnetic field of the permanent magnet falls as in hint 1 below with \(I\) replaced by some constant \(I_0\). Find the velocity of the magnet as a function of time, if the magnet is released at \(t=0\). Hint 1: The magnitude of a magnetic field caused by a current loop of radius \(\rho\) along the axis of the loop is: \[B = \frac{\mu_0 I \rho}{2(\rho^2+z^2)^{3/2}}.\] where \(z\) is the distance along the axis of the loop and \(I\) is the current in the loop. Hint 2: The force between two magnetic dipole moments is \[F = |\nabla (\vec{m} \cdot \vec{B})| \] where the \(B\) field is due to one dipole moment and \(m = IA\) is the the other dipole moment, with \(I\) the effective current and \(A\) the cross-sectional area treating the second dipole as a current loop. Solution: At a distance \(r\) down the tube, the magnitude of the rate of change of magnetic flux through a circular cross-section of the tube is: \[\frac{d\Phi_B}{dt} = A\frac{dB}{dt} = \frac{d}{dt} \left(\frac{\mu_0 I_0 \sqrt{A/\pi}}{2((A/\pi)+r^2(t))^{3/2}}\right) =-\frac{3\mu_0 I_0 r(t) v(t)\sqrt{A} \pi^2}{2(A+\pi r(t)^2)^{5/2}}.\] where \(I_0\) is a constant that describes the effective strength of the permanent magnet as a magnetic dipole. The magnitude of the current induced in the copper ring bounding this cross-section is therefore: \[I(t) = \frac{3\mu_0 I_0 r(t) v(t)\sqrt{A} \pi^2}{2R(A+\pi r(t)^2)^{5/2}}.\] Below the falling magnet, the magnetic flux is increasing over time. The direction of the current thus creates a magnetic field opposing the field of the permanent magnet, which will manifest itself as a repulsive force. Above the falling magnet, the magnetic flux is decreasing over time. The direction of the current thus creates a magnetic field in the same direction as the permanent magnet, which will manifest itself as an attractive force. These two effects slow the rate of fall of the permanent magnet. Using hint 2, the force between the dipole moment of a copper ring and the magnetic field of the permanent magnet is: \[F = AI(t) |\nabla (B(t)| = \frac{3\mu_0 I_0 r(t) v(t)A^{3/2} \pi^2}{2R(A+\pi r(t)^2)^{5/2}} \left( \frac{3\mu_0 I_0 \sqrt{A/\pi}r(t)}{2(A/\pi + r(t)^2)^{5/2}} \right) = \frac{9\mu_0^2 I_0^2 r(t)^2 v(t) A^2 \pi^4}{4R(A+ \pi r(t)^2)^{5}} .\] This is just the force due to a single current ring on the permanent magnet. To find the total force on the permanent magnet, one must integrate in both directions of \(r(t)\) above and below the permanent magnet. Keeping in mind that the force above is just a magnitude and that the function for the force is even, it suffices to compute the force due to one direction and double it: \[ \begin{align} F_{\text{total}} &=2 \int_0^{\infty} \frac{9\mu_0^2 I_0^2 r(t)^2 v(t) A^2 \pi^4}{4R(A+ \pi r(t)^2)^{5}} dr =\frac{9\mu_0^2 I_0^2 v(t) A^2 \pi^4}{2R} \int_0^{\infty} \frac{r(t)^2}{(A+ \pi r(t)^2)^{5}} dr \\ &= \frac{9\mu_0^2 I_0^2 v(t) A^2 \pi^4}{2R} \left(\frac{5}{256 \sqrt{\pi} A^{7/2}} \right) = \frac{45\mu_0^2 I_0^2\pi^{3/2}}{512 R A^{3/2}} v(t) \end{align} \] The form of the force is a viscous damping force proportional to the velocity, which is a good check of the validity of the above discussion. Finally, writing down Newton's second law will allow the velocity to be found. The magnet is accelerated by gravity, which is opposed by the magnetic force written above: \[Mv'(t) = Mg - \frac{45\mu_0^2 I_0^2\pi^{3/2}}{512 R A^{3/2}} v(t).\] Define the constant, dependent on the parameters \(I_0\), \(R\), and \(A\): \[\kappa = \frac{45\mu_0^2 I_0^2\pi^{3/2}}{512 R A^{3/2}}.\] Then Newton's second law reads: \[Mv'(t) = Mg - \kappa v(t).\] This first order ODE, with the initial condition \(v(0) = 0\) because the permanent magnet is dropped from rest, is solved by: \[v(t) = \frac{Mg}{\kappa} \left(1- e^{-\frac{\kappa t}{M}}\right) = \frac{512 Mg R A^{3/2}}{45\mu_0^2 I_0^2\pi^{3/2}} \left(1- e^{-\frac{\kappa t}{M}}\right) .\] At late times, the permanent magnet approaches a terminal velocity \(\frac{Mg}{\kappa}\) exponentially quickly. Furthermore, if the permanent magnet is weak (\(\kappa \approx 0\)) the RHS above can be Taylor expanded: \[v(t) \approx \frac{Mg}{\kappa} \left(\frac{\kappa t}{M} - \frac{\kappa^2 t^2}{2M^2} \right) = gt - \frac{\kappa g t^2}{2M} .\] This provides a small negative correction at early times to the usual linear growth \(gt\) of the velocity, as expected. Many approximations have been made throughout this computation: the approximation of the magnetic dipole as a current loop, the approximation that the tube is long and the cross-section small so that edge effects are insignificant, and the assumption that the interaction of the magnet with each current ring can be modeled by the dipole-dipole interaction well. Nevertheless, the analytic expression obtained above captures the qualitative behavior of the physical scenario very well. If the cross-section of the tube is wide or the resistance high, the induced current is small and the damping is very slow with a higher terminal velocity. If \(I_0\) is large, the permanent magnet is very strong, inducing a strong damping effect, consistent with the small terminal velocity and high speed of damping found above.

The same effect is visible in MRI scanners, which are like tubes that have much more powerful magnetic fields. Below, Lenz's law is demonstrated in the slow motion of an aluminum bar in the magnetic field of an MRI:

in real time [3]." /> The powerful magnetic field of an MRI induces a magnetic field from the aluminum bar that causes a force acting against gravity. The bar is falling in real time [3].

Compare the speeds at which a permanent magnet and a piece of metal of the same shape and mass fall through a conducting tube.

The permanent magnet will:

[1] Purcell, E.M. Electricity and Magnetism . Third Edition. Cambridge University Press, 2013.

[2] Excerpted from https://www.youtube.com/watch?v=keMpUaoA3Tg using GIPHY.com.

[3] Excerpted from https://www.youtube.com/watch?v=liDjr439-fY using GIPHY.com.

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23.2 Faraday’s Law of Induction: Lenz’s Law

Learning objectives.

By the end of this section, you will be able to:

• Calculate emf, current, and magnetic fields using Faraday’s Law.
• Explain the physical results of Lenz’s Law

Faraday’s and Lenz’s Law

Faraday’s experiments showed that the emf induced by a change in magnetic flux depends on only a few factors. First, emf is directly proportional to the change in flux Δ Φ Δ Φ . Second, emf is greatest when the change in time Δ t Δ t is smallest—that is, emf is inversely proportional to Δ t Δ t . Finally, if a coil has N N turns, an emf will be produced that is N N times greater than for a single coil, so that emf is directly proportional to N N . The equation for the emf induced by a change in magnetic flux is

This relationship is known as Faraday’s law of induction . The units for emf are volts, as is usual.

The minus sign in Faraday’s law of induction is very important. The minus means that the emf creates a current I and magnetic field B that oppose the change in flux Δ Φ Δ Φ —this is known as Lenz’s law . The direction (given by the minus sign) of the emf is so important that it is called Lenz’s law after the Russian Heinrich Lenz (1804–1865), who, like Faraday and Henry, independently investigated aspects of induction. Faraday was aware of the direction, but Lenz stated it so clearly that he is credited for its discovery. (See Figure 23.7 .)

Problem-Solving Strategy for Lenz’s Law

To use Lenz’s law to determine the directions of the induced magnetic fields, currents, and emfs:

• Make a sketch of the situation for use in visualizing and recording directions.
• Determine the direction of the magnetic field B.
• Determine whether the flux is increasing or decreasing.
• Now determine the direction of the induced magnetic field B. It opposes the change in flux by adding or subtracting from the original field.
• Use RHR-2 to determine the direction of the induced current I that is responsible for the induced magnetic field B.
• The direction (or polarity) of the induced emf will now drive a current in this direction and can be represented as current emerging from the positive terminal of the emf and returning to its negative terminal.

For practice, apply these steps to the situations shown in Figure 23.7 and to others that are part of the following text material.

Applications of Electromagnetic Induction

There are many applications of Faraday’s Law of induction, as we will explore in this chapter and others. At this juncture, let us mention several that have to do with data storage and magnetic fields. A very important application has to do with audio and video recording tapes . A plastic tape, coated with iron oxide, moves past a recording head. This recording head is basically a round iron ring about which is wrapped a coil of wire—an electromagnet ( Figure 23.8 ). A signal in the form of a varying input current from a microphone or camera goes to the recording head. These signals (which are a function of the signal amplitude and frequency) produce varying magnetic fields at the recording head. As the tape moves past the recording head, the magnetic field orientations of the iron oxide molecules on the tape are changed thus recording the signal. In the playback mode, the magnetized tape is run past another head, similar in structure to the recording head. The different magnetic field orientations of the iron oxide molecules on the tape induces an emf in the coil of wire in the playback head. This signal then is sent to a loudspeaker or video player.

Similar principles apply to computer hard drives, except at a much faster rate. Here recordings are on a coated, spinning disk. Read heads historically were made to work on the principle of induction. However, the input information is carried in digital rather than analog form – a series of 0’s or 1’s are written upon the spinning hard drive. Today, most hard drive readout devices do not work on the principle of induction, but use a technique known as giant magnetoresistance . (The discovery that weak changes in a magnetic field in a thin film of iron and chromium could bring about much larger changes in electrical resistance was one of the first large successes of nanotechnology.) Another application of induction is found on the magnetic stripe on the back of your personal credit card as used at the grocery store or the ATM machine. This works on the same principle as the audio or video tape mentioned in the last paragraph in which a head reads personal information from your card.

Another application of electromagnetic induction is when electrical signals need to be transmitted across a barrier. Consider the cochlear implant shown below. Sound is picked up by a microphone on the outside of the skull and is used to set up a varying magnetic field. A current is induced in a receiver secured in the bone beneath the skin and transmitted to electrodes in the inner ear. Electromagnetic induction can be used in other instances where electric signals need to be conveyed across various media.

Another contemporary area of research in which electromagnetic induction is being successfully implemented (and with substantial potential) is transcranial magnetic simulation. A host of disorders, including depression and hallucinations can be traced to irregular localized electrical activity in the brain. In transcranial magnetic stimulation , a rapidly varying and very localized magnetic field is placed close to certain sites identified in the brain. Weak electric currents are induced in the identified sites and can result in recovery of electrical functioning in the brain tissue.

Sleep apnea (“the cessation of breath”) affects both adults and infants (especially premature babies and it may be a cause of sudden infant deaths [SID]). In such individuals, breath can stop repeatedly during their sleep. A cessation of more than 20 seconds can be very dangerous. Stroke, heart failure, and tiredness are just some of the possible consequences for a person having sleep apnea. The concern in infants is the stopping of breath for these longer times. One type of monitor to alert parents when a child is not breathing uses electromagnetic induction. A wire wrapped around the infant’s chest has an alternating current running through it. The expansion and contraction of the infant’s chest as the infant breathes changes the area through the coil. A pickup coil located nearby has an alternating current induced in it due to the changing magnetic field of the initial wire. If the child stops breathing, there will be a change in the induced current, and so a parent can be alerted.

Making Connections: Conservation of Energy

Lenz’s law is a manifestation of the conservation of energy. The induced emf produces a current that opposes the change in flux, because a change in flux means a change in energy. Energy can enter or leave, but not instantaneously. Lenz’s law is a consequence. As the change begins, the law says induction opposes and, thus, slows the change. In fact, if the induced emf were in the same direction as the change in flux, there would be a positive feedback that would give us free energy from no apparent source—conservation of energy would be violated.

Example 23.1

Calculating emf: how great is the induced emf.

Calculate the magnitude of the induced emf when the magnet in Figure 23.7 (a) is thrust into the coil, given the following information: the single loop coil has a radius of 6.00 cm and the average value of B cos θ B cos θ (this is given, since the bar magnet’s field is complex) increases from 0.0500 T to 0.250 T in 0.100 s.

To find the magnitude of emf, we use Faraday’s law of induction as stated by emf = − N Δ Φ Δ t emf = − N Δ Φ Δ t , but without the minus sign that indicates direction:

We are given that N = 1 N = 1 and Δ t = 0 . 100 s Δ t = 0 . 100 s , but we must determine the change in flux Δ Φ Δ Φ before we can find emf. Since the area of the loop is fixed, we see that

Now Δ ( B cos θ ) = 0 . 200 T Δ ( B cos θ ) = 0 . 200 T , since it was given that B cos θ B cos θ changes from 0.0500 to 0.250 T. The area of the loop is A = πr 2 = ( 3 . 14 . . . ) ( 0 . 060 m ) 2 = 1 . 13 × 10 − 2 m 2 A = πr 2 = ( 3 . 14 . . . ) ( 0 . 060 m ) 2 = 1 . 13 × 10 − 2 m 2 . Thus,

Entering the determined values into the expression for emf gives

While this is an easily measured voltage, it is certainly not large enough for most practical applications. More loops in the coil, a stronger magnet, and faster movement make induction the practical source of voltages that it is.

PhET Explorations

Faraday's electromagnetic lab.

Play with a bar magnet and coils to learn about Faraday's law. Move a bar magnet near one or two coils to make a light bulb glow. View the magnetic field lines. A meter shows the direction and magnitude of the current. View the magnetic field lines or use a meter to show the direction and magnitude of the current. You can also play with electromagnets, generators and transformers!

Click to view content .

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Electromagnetic induction is governed by two fundamental laws – Faraday’s Law and Lenz’s Law. Faraday’s Law establishes a relationship between the induced emf (ε) and the magnetic flux rate (dφ/dt) in a conducting coil of N turns. It is given by the following formula.

ε = – N dφ/dt

However, the equation does not state anything about the conservation of energy . Lenz’s Law can explain energy conservation and the negative sign in Faraday’s Law equation.

What is Lenz’s Law

Lenz’s Law states,

“The polarity of the induced emf is such that it opposes the change in magnetic flux that produced it.”

When a magnetic field induces a current in a conducting coil, the induced current generates its magnetic field, opposite to the inducing magnetic field. In other words, an induced current will always oppose the motion that started it in the first place. Lenz’s Law is significant since it can determine the direction of the induced current and the magnetic field induced by the current.

The change in the magnetic flux around a conducting coil may be caused in several ways:

• Change the magnetic field strength
• Move the magnet toward or away from the coil
• Move the coil into or out of the magnetic field
• Rotate the coil relative to the magnet

Lenz’s Law is named after German physicist Heinrich Friedrich Lenz after he deduced it in 1834.

Lenz’s Law and Conservation of Energy

To obey the conservation of energy, the direction of the current induced via Lenz’s law must create a magnetic field that opposes the magnetic field that created it in the first place. The direction of this induced magnetic field is determined by the right-hand rule .

Suppose the current did not oppose the magnet’s magnetic field. Then, the induced magnetic field would be in the same direction as the inducing magnetic field. These two magnetic fields would add up and create a larger magnetic field. This larger magnetic field would induce another current in the coil twice the magnitude of the original current. This induced current will generate another magnetic field, and the process will continue. Thus, an endless loop of induced currents and magnetic fields would violate the energy conservation law. Therefore, Lenz’s Law is a consequence of the energy conservation principle.

Applications of Lenz’s Law

Lenz’s law can be applied to the following devices:

• Electric generators
• Electromagnetic braking
• Induction cooktop
• Eddy current equalizers
• Eddy current dynamometers
• Microphones
• Card readers

Example Problems and Solutions

Problem 1: Calculate the magnitude of the induced emf when the magnet is thrust into a coil. The following information is given: the single loop coil has a radius of 5 cm, and the average value of the complex magnetic field component B cos θ increases from 0.1 T to 0.5 T in 0.2 s.

r = 5 cm = 0.05 m

A = πr 2 = π (0.05m) 2 = 0.0079 m 2

(B cos θ) initial = 0.1 T

(B cos θ) final = 0.5 T

ΔB = (B cos θ) final – (B cos θ) initial = 0.5 T – 0.1 T = 0.4 T

From Faraday’s law,

|ε| = N Δφ/Δt

or, |ε| = N A Δ(B cos θ)/Δt

or, |ε| = 1 x 0.0079 m 2 x 0.4 T/0.2 s = 0.016 Tm 2 /s = 16 mV

Problem 2: A circular coil of wire with 450 turns and a radius of 8 cm is placed horizontally on a table. A uniform magnetic field pointing directly into the wire and perpendicular to its surface is slowly turned on, such that the strength of the magnetic field can be expressed as a function of time as B(t) = 0.01(Ts -2 ) x t 2 . (A) What is the total emf in the coil as a function of time? (B) In which direction does the current flow?

B(t) = 0.01(Ts -2 ) x t 2

r = 8 cm = 0.08 m

A = πr 2 = π(0.08 m) 2 = 0.02 m 2

or, ε = – 450 x d(BA)/dt

or, ε = – 450 x 0.02 m 2 x d (0.01(Ts -2 ) x t 2 )/ dt

or, ε = – 0.09 x 2t Tm 2 /s 2

or, ε = – 0.18t T/s

(B) The current will be clockwise looking from the top.

• Lenz’s Law – Hyperphysics.phy-astr.gsu.edu
• Lenz’s Law – Isaacphysics.org
• Lenz’s Law – Farside.ph.utexas.edu
• Lenz’s Law – Openpress.usask.ca
• Lenz Law vs. Faraday’s Law: How Do They Govern Crosstalk and EMI? – Resources.pcb.cadence.com
• Faraday’s and Lenz’s Law – Usna.edu
• Faraday’s Law, Lenz’s Law, and the Lorentz Force – Vanderbilt.edu
• Lenz’s Law – Phys.libretexts.org

Article was last reviewed on Thursday, February 2, 2023

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Heinrich Friedrich Emil Lenz was a Russian physicist, working at the University of St. Petersburg, Russia. He formulated Lenz’s law in 1834. This law predicts the direction of the current and the induced voltage in a coil held in a magnetic field.

Lenz’s law – Statement

The direction of an induced e.m.f. is always such that it tends to set up a current opposing the motion or the change of flux responsible for inducing that e.m.f.

EMF is induced in a coil when there is a relative motion between the coil and a magnetic field. So, according to this law, the direction of induced emf or current is always such that it opposes the change in the magnetic field . This may be a little difficult to understand in the beginning.

Explanation

Assume that we have a coil and a permanent magnet. Here you must remember the following points.

Lenz’s law states that the direction of the induced current will be such that the field-2 produced by it opposes field-1.

As you notice in the above illustration, when the permanent magnet (Field-1) is moved towards the coil, an EMF is induced in it which produces a current(I). The polarity of EMF will be such that the magnetic field (Field-2) produced by the current(I) opposes the further motion of Field-1 towards it.

Similarly, when the permanent magnet is moved away from the coil, the polarity of the induced EMF will be such that Field-2 opposes the motion of Field-1 away from it.

Here the ‘ motion of permanent magnet’ is the cause and the direction of induced current sets up a magnetic field that opposes the motion of the permanent magnet.

Lenz’s law equation

Lenz’s law is based on Faraday’s law of electromagnetic induction . The combined equation for these two laws are:

Where, N is the number of turns of coil, ΔΦ is the change in magnetic flux through the coil in time Δt. The minus sign indicates the opposition to the change in magnetic field.

Experiment explaining Lenz law

This phenomenon is absent when the bar magnet is moved towards or away from the non enclosed ring since the induced current cannot enclose the magnet.

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Really its a very good effort to bring the concept to understand each and everyone. Thank you for sharing this wonderful video and explanations.

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Collection of Physics Experiments

Levitating ring – lenz's law demonstration, experiment number : 2100, goal of experiment.

The experiment shows one of the possible demonstrations of Lenz’s law.

If a conductor is placed in a magnetic field, voltage is induced in the conductor. The magnitude of this voltage is given by Faraday's law of electromagnetic induction:

where Δ Φ  is change in magnetic induction flux over time t .

If the conductor is closed, it carries an induced current. The direction of this induced current is described by Lenz’s law:

“Induced current in a closed circuit has such a direction that by its magnetic field it counteracts the change in magnetic induction flow that has caused it.”

In our case, the variable magnetic field will be generated by the coil connected to the alternating current. A lightweight aluminium ring placed on the coil core (see Fig. 1 on the left) will act as the closed conductor. Since the ring is closed, induced current will flow through it. Its direction will be, according to Lenz’s law, such that the magnetic field that surrounds the ring will be acting against the change of the magnetic flux that caused it – therefore, the magnetic field of the ring will be repelled from the magnetic field of the coil. The ring is relatively light and made of a conductive material, the induced current will therefore be so large that the ring will levitate due to the repulsive magnetic force.

A different scenario occurs when we use a cut ring (in Figure 1 on the right): voltage will be induced in the ring, however no current will be induced since the ring is not closed. Therefore, no magnetic field will be generated around it and the ring will not levitate.

• coil with 300 turns
• laminated U core
• long I core
• AC 42 V power supply
• two aluminium rings (one closed, one cut)
• connecting wires
• Put the coil on one side of the U core. Use the I core to extend this side.
• Connect the coil to an AC power supply of approximately 40 V.
• Place the aluminium ring on the extended core, turn on the power supply and observe that the ring rises and floats a few centimetres above the coil.

After performing and explaining the experiment, it is appropriate to propose a problem experiment to the students – instead of the closed ring, place a cut ring on the core in such a way, that the students cannot see the cut part. Let them explain this problem (see Pedagogical notes).

Sample result

The sample result can be seen in the video:

Problem experiment

The following video shows an experiment with another ring, which does not levitate. The video can be used as a problem task for students (see Pedagogical notes).

Pedagogical notes

The experiment with a cut ring is suitable as a problem task – the teacher will show the students the experiment so that the cut is not visible, the students’ task is to suggest hypotheses why the ring does not levitate. If possible, it is advisable for the teacher to carry out the experiment with the same layout and in the same order as the experiment with the uncut ring to make sure that the problem is not, for example, in broken conductors. The students should realize that the condition for magnetic field generation around the ring is that current must flow through it; induced voltage will not make the ring to levitate.

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What is Lenz’s Law?

Lenz’s Law named after the physicist Emil Lenz was formulated in 1834. It states that the direction of the current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field.

When a current is induced by a magnetic field, then the magnetic field produced by the induced current will create its magnetic field. Thus, this magnetic field will be opposed by the magnetic field that created it. 

Lenz's law is based on Faraday's law of Induction which says, a changing magnetic field will induce a current in a conductor whereas Lenz's law tells us the direction of the induced current, which opposes the initial changing magnetic field which produced it. Hence, this is signified in the formula for Faraday's law by the negative sign.

\[ \epsilon = -\frac{d\Phi _{B}}{dt}\]

The magnetic field can be changed by changing its strength or by either moving the magnet towards or away from the coil, or moving the coil in or out of the magnetic field.

Hence we can say that the magnitude of the electromagnetic field induced in the circuit is proportional to the rate of change of flux.

\[ \epsilon \alpha  \frac{d\Phi _{B}}{dt}\]

Lenz Law Formula:

According to Lenz's law, when an electromagnetic field is generated by a change in magnetic flux, the polarity of the induced electromagnetic field produces an induced current whose magnetic field opposes the initial changing magnetic field which produced it.

The formula for Lenz law is shown below:

\[ \epsilon = -N(\frac{d\Phi _{B}}{dt})\]

\[ \epsilon \] = induced EMF

\[d\Phi _{B}\]  =  change in magnetic flux

N = number of turns in the coil

Lenz law applications:

The applications of lenz's law include:.

When a source of an electromagnetic field is connected across an inductor, a current starts flowing through it. The back electromagnetic field will oppose this increase in current through the inductor. To establish the flow of current, the external source of the electromagnetic field has to do some work for overcoming this opposition.

Lenz’s law is used in electromagnetic brakes and induction cooktops.

It is also applied to electric generators, AC generators.

Eddy Current Balances

Metal detectors

Eddy current dynamometers

Braking systems on train

Card Readers

Microphones

Lenz Law Experiment:

To find the direction of the induced electromotive force and current we use Lenz’s law. Some experiments are below.

First Experiment:

In the first experiment, when the current in the coil flows in the circuit, the magnetic field lines are produced. As the current flows through the coil increases, the magnetic flux will increase. The direction of the flow of induced current would be such that it opposes when the magnetic flux increases.

Second Experiment:

In the second experiment, when the current-carrying coil is wound on an iron rod with its left end behaving as N-pole and is moved towards the coil S, an induced current will be produced.

Third Experiment:

In the third experiment, the coil is pulled towards the magnetic flux, the coil linked it goes on decreasing which means that the area of the coil inside the magnetic field decreases. 

According to Lenz’s law, the motion of the coil is opposed when the induced current is applied in the same direction.

To produce current, force is exerted by the magnet in the loop. To oppose the change a force must be exerted by the current on the magnet.

An example of Lenz Law:

In a copper or aluminum pipe, there is the presence of large magnetic fields that cause counter-rotating currents. Dropping the magnet through the pipe demonstrates this particular phenomenon. When the magnet is being dropped within the pipe it tends to descend at a rate that is lower than when it is dropped outside the pipe. Here there is a current induced which can be determined using the right-hand rule.

FAQs on Lenz Law

1. How does Lenz’s law relate to the conservation of energy?

Lenz’s law is based on the law of conservation of energy. From the definition of Lenz’s law, it is seen that the current will always flow in the opposite direction of the object or the cause that has produced it. Therefore there is more work that needs to be done to go against an opposing force. This work done against the opposing force hence results in a change in the magnetic flux because of which the current is induced. The extra work that is done is converted to electrical energy which is the law of conservation of energy.

2. What is the history of Lenz law?

Heinrich Lenz is also referred to as Emil Lenz. He was a Baltic German physicist who may not have reached his fame in the early 1900s unlike his peers Michael Faraday who was known to solve a lot of mysteries related to electromagnetism. The law received the name Lenz for the fast and comprehensive documentation that the experiments had along with the dedication to the scientific method which was not common at that time. This law also forms an important part of Faraday’s laws and hence tells about the direction in which the current tends to flow.

3. How do Lenz law and Faraday's law relate to each other?

Lenz law is encapsulated in Faraday’s laws as it tells us why the direction in which the induced current tends to flow. The easiest way to state the Lenz law is that the change in magnetic flux tends to induce a current which is in a direction that is opposite to the object that has generated it. It can hence also be said that when the current flows, it creates its own magnetic field. The direction of the current will be such that the new magnetic field is in the opposed direction of the flux changes that have created it. This law is part of the Lenz law as it consists of a negative sign that indicates the EMF opposes the original change in magnetic flux.

4. What are eddy currents and how are they understood by using Lenz law?

Eddy’s current is a small electric current that follows Lenz law. While it is used to refer to small currents it actually generates a large looping current in conductors. When a conductor is moved through the magnetic field there is a production of electric currents being generated which is in line with Lenz’s law and counteracts the effect of motion leading to magnetic damping. This sort of motion where the field that is induced works against the motion through which it is created tends to be heavily used in magnetic braking systems such as roller coasters.

5. Why should students learn Lenz’s law?

Lenz’s law has a variety of applications and is quite important in the history of currents. This law that tells students a lot regarding the concepts that are used in various machines helps students to learn about these machines and how they work. With the help of this law, there is basic knowledge regarding how the conservation of energy takes place while there is opposed motion being observed.

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Lenz’s Law

Lenz law was given by the German scientist Emil Lenz in 1834 this law is based on the principle of conservation of energy and is in accordance with Newton’s third law. Lenz law is used to give the direction of induced current in the circuit.

In this article, let’s learn about Lenz law its formula, experiments, and others.

What is Lenz’s law?

The general definition of Lenz’s Law is,

“The induced current in a circuit due to Electromagnetic Induction always opposes the change in magnetic flux.”

It is a scientific law that specifies the direction of induced current but states nothing about its magnitude. The magnetic field associated with the closed circuit amplifies the induced current flow in such a way that it creates a magnetic field in the opposite direction of the original magnetic field. Thus, opposing the cause which produced it and stating its similarity with Newton’s third law.

Lenz’s Law Formula

Lenz’s Law formula is stated from Faraday’s Law of Electromagnetic Induction . According to this law, EMF on the coil is calculated as,

E = -N(d∅/dt) where, negative sign indicates that the direction of induced emf is such that it opposes the change in magnetic flux) E is the electromotive force N is number of loops the coil made d∅ is the change in magnetic flux dt is change in time

Lenz’s Law Experiment

Lenz’s law provides the direction of the induced electromotive force and current induced in the closed circuit. The experiments proved by Lenz to state its theory are,

The image given below shows a metallic conductor placed in a magnetic field.

First Experiment

First experiment by Lenz proved that the current flowing in the coil produces a magnetic field in the circuit and the strength of the magnetic field increases with an increase in the strength of the induced current. Also, this magnetic field produced opposes the original magnetic field i.e. the direction of the induced current is opposite to the original magnetic field.

Second Experiment

Second experiment by Lenz states that the iron rod wound by the current-carrying wire and its left end behave as N-pole if moves towards the coil an induced current is produced in the coil.

Third Experiment

Third experiment by Lenz states that if the coil is pulled towards the magnetic flux, the magnetic flux linked with the coil decreases as the area of the coil inside the magnetic field decreases. Now the induced current in the same direction opposes the motion of the coil according to Lenz’s law.

From the above experiments,  we can conclude that the current is produced when the magnet exerts the force in the loop and to resist the change, the current exerts a force on the magnet.

What is Electromagnetic Induction?

It is the phenomenon of production of induced emf due to a change of magnetic flux (number of magnetic field lines) connected to a closed circuit called electromagnetic induction.

Lenz’s Law Explanation

Lenz’s law is easily explained by two cases.

As shown in the figure, when the North pole bar magnet is moved towards the coil, the induced current in the coil flows in the anticlockwise direction, when we see it from the magnet side. The face of the coil develops north polarity. As we know, that same pole repels, so the north pole-north pole repels. So, it opposes the motion of the North pole of a magnet.

Conclusion: The motion of the magnet increases the flux through the coil and flux will be generated in the opposite direction by the induced current.

As shown in the figure when the North pole of a bar magnet is taken away from the coil, the induced current in the coil flows in the clockwise direction. The face of the coil develops South polarity. We know that opposite poles attract. So, the north pole and south polarity attract each other.

Conclusion: The motion of the magnet decreases the flux through the coil. The flux is generated in the same direction by induced current, hence opposing and increasing the flux.

Lenz’s Law Applications

Lenz’s Law finds its importance in various cases and some of the most common  uses of Lenz’s law are,

• The braking system in trains works on the principle of Lenz’s law
• AC generators work on the principle of Lenz’s law
• Eddy currents are balanced using Lenz’s Law
• Metal Detectors, Card readers, and many other electronic devices use the concept of Lenz’s law for their application.

Lenz’s law and Law of Conservation of Energy

Lenz’s law is a consequence of the law of conservation of energy . The law of conservation of energy states that energy can neither be created nor be destroyed, but it can be changed from one form to another form. Lenz’s law states that the direction of current is such that it opposes the change in the magnetic flux. So, extra effort is required to do work against opposing forces. This extra work leads to periodic changes in magnetic flux hence more current is induced. Thus, the extra effort gets converted into electrical energy only, which is nothing but the law of conservation of energy.

The magnetic flux increases as the North Pole of the magnet approaches it and drops as it is driven away in the activity above. In the first scenario, opposing the cause involves moving the magnet, and the face facing the coil gains North Polarity. The magnet’s north pole and the coil’s north pole repel each other. To counteract the force of repulsion, mechanical action must be done to bring the magnet towards the coil. This mechanical energy is transformed into electrical energy. Due to Joule’s Effect, this electrical energy is turned into heat energy.

The image given below shows the magnetic flux linked with the coil when a magnet is taken close or away from the coil.

When the magnet is moved away from the coil, the coil’s nearer face obtains south polarity. In this instance, the produced emf will oppose the magnet’s outward motion. To resist the force of attraction between the North Pole of the magnet and the South Pole of the coil, mechanical labour must be done once more. This labour is transformed into electrical energy.

There is no mechanical work done if the magnet is not moved, hence no emf is induced in the coil.

As a result, Lenz’s Law is consistent with the law of conservation of energy.

Also, Check

Electromagnetic Induction Experiments of Faraday and Henry

FAQs on Lenz’s Law

Q1: what is lenz’s law.

Lenz’s law states that the Induced current in a coil is in that direction which opposes the change in magnetic flux through the coil.

Q2: Where is Lenz’s law used?

Lenz’s law is used to find the direction of induced current in any circuit. It works in accordance with Newton’s third law.

Q3: What is the difference between Lenz’s law and Faraday’s law?

The difference between Faraday’s law and Lenz’s law can be explained through, Lenz’s law states the direction of an induced current. Faraday’s law states that the magnitude of the emf induced in a circuit is proportional to the rate of change of magnetic flux.

Q4: What is the History of Lenz law?

A Baltic German physicist Heinrich Lenz proposed the Lenz Law in early 1900s

Q5: Which law gives the direction of current in an AC generator?

Lenz’s law is used to provide the direction of current in an AC generator.

Q6: How is Lenz’s law related to the law of conservation of energy?

Lenz’s law states that the induced EMF in the coil always opposes the cause which produces it which is in accordance with the law of conservation of energy.

Q7: What does the negative sign indicate in Lenz’s law?

The negative sign in Lenz’s law indicates that “the induced emf produced in the coil due to electromagnetic induction is opposite to the cause which creates the current in the coil.”

Q8: Which principle of conservation derives the Lenz Law?

Lenz law is derived from the law of conservation of energy.

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Jakob Michael Reinhold Lenz

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Jakob Michael Reinhold Lenz (born January 12, 1751, Sesswegen, Livonia, Russian Empire [now Cesvaine, Latvia]—found dead May 24, 1792, Moscow , Russia) was a Russian-born German poet and dramatist of the Sturm und Drang (Storm and Stress) period, who is considered an important forerunner of 19th-century naturalism and of 20th-century theatrical Expressionism .

Lenz studied theology at Königsberg University but gave up his studies in 1771 to travel to Strasbourg as a tutor and companion to two young barons von Kleist. In Strasbourg he became a member of Goethe ’s circle and was strongly influenced by the Sturm und Drang sentiments of that group of dramatists. Lenz made his reputation with plays from the Strasbourg years, an eccentric didactic comedy, Der Hofmeister oder Vortheile der Privaterziehung (published 1774, performed 1778, Berlin; “The Tutor, or the Advantages of Private Education”), and his best play, Die Soldaten (performed 1763, published 1776; “The Soldiers”). His plays have dramatic and comic effects arising from strong characters and the swift juxtaposition of contrasting situations. Anmerkungen übers Theater (1774; “Observations on the Theatre”) contains a translation of Shakespeare ’s Love’s Labour’s Lost and outlines Lenz’s theories of dramaturgy, summarizing conceptions of theatre that he shared with other members of the Sturm und Drang movement. These include contempt for classical conventions, particularly the unities of time and place, and a search for utterly realistic depiction of character.

Consumed by the ambition to become Goethe’s equal, Lenz made himself ridiculous by imitating both Goethe’s writing style and his personal life in Strasbourg and at court in Weimar, where Lenz followed Goethe in 1776. His eccentricities were thought to be harmless and amusing until a tactless parody angered Duke Charles Augustus , who therefore expelled Lenz from the court in disgrace. Lenz, showing signs of mental illness , was eventually placed in the care of the Lutheran pastor Johann Friedrich Oberlin . (These weeks in Oberlin’s household supplied the material for Georg Büchner ’s novella Lenz [1839].) Lenz later returned to Russia , spending the remaining years of his life in aimless drifting and poverty and, eventually, in insanity. He was found dead in a street in Moscow.