Lenzs Law - Definition, Formula, Examples, Applications, FAQs

Lenz Law:

Lenz law is associated with, named after Emil Lenz, is based on the conservation of energy principle and Newton's third law. It is the most practical way for determining the induced current's direction. It asserts that the direction of an induced current is always in opposition to the circuit or magnetic field change that causes it.

State Lenz law of electromagnetic induction and define Lenz law.

Lenz Law Definition or Lenz Law Statement: “When current runs through the loop, the induced electromotive force with various polarities produces a current whose magnetic field oppose change in magnetic flux through loop, ensuring that the original flux is preserved.”

Also read -

• NCERT Solutions for Class 11 Physics
• NCERT Solutions for Class 12 Physics
• NCERT Solutions for All Subjects

Lenz law formula:

The formula of Faraday's law is based on Lenzs law. Lenz law provides the negative sign in this case. It is given by the formula:

Emf=−N(Δϕ/Δt)

The induced voltage is referred to as Emf (also known as electromotive force).

The number of loops is N.

Δϕ shift in the magnetic flow

Δt is the passage of time.

The induced electromotive force and the rate of change in magnetic flux have the same sign, indicating that they are in opposing directions.

This indicates that the direction of an induced field's back EMF opposes the changing current that causes it. D.J. Griffiths summed it up this way: "Nature despises change."

It's a qualitative law that describes the direction of generated current but not the amplitude of it. Many electromagnetic phenomena, such as direction of voltage induced in an inductor by changing current, or the drag force of eddy currents imparted on moving objects in a magnetic field, are predicted by Lenz law.

Also read :

• NCERT notes Class 12 Physics Chapter 6 Electromagnetic Induction
• NCERT solutions for Class 12 Physics Chapter 6 Electromagnetic Induction
• NCERT Exemplar Class 12 Physics Solutions Chapter 6 Electromagnetic Induction

Lenz Law Examples:

In a copper or aluminium pipe, large magnetic fields can cause counter-rotating currents. Dropping the magnet through the pipe demonstrates this. When the magnet is dropped within the pipe, it descends at a slower rate than when it is dropped outside the pipe.

According to Faraday's law, when a voltage is formed by a change in magnetic flux, the induced voltage's polarity which produces current whose magnetic field oppose change which is produced by itself. The magnetic flux in any loop of wire is always kept constant by the induced magnetic field inside the loop.

The right-hand rule can be used to determine the direction of an induced current, which shows which direction of current flow creates a magnetic field that opposes the direction of changing flux through the loop. When the flux is growing in the instances below, the induced field opposes it. If it is decreasing, the induced field opposes the change by acting in the same direction as the applied field.

Applications of Lenz law

Lenz has a plethora of legal uses. The following are a few of them:

1. Balances of eddy currents
2. Metal detectors are used to detect metal.
3. Eddy current dynamometers.
4. Train AC generators have braking systems.
5. Readers of credit cards
6. Microphones

Experiment of lenz law of electromagnetic induction:

Lenz law is used to determine the direction of the induced electromotive force and current. In accordance with Lenz's theory, he performed some experiments.

NCERT Physics Notes:

• NCERT Notes Class 11th Physics
• NCERT Notes Class 12th Physics
• NCERT Notes For All Subjects

The Initial Experiment

He concluded in the first experiment that magnetic field lines are formed when electricity in the coil flows in the circuit. The magnetic flux will grow as the current flowing through the coil increases. When the magnetic flux increases, the flow of induced current will be in the opposite direction.

Experiment number 2

In the second experiment, he discovered that an induced current is produced when the current-carrying coil is wound on an iron rod with its left end acting as an N-pole and advanced towards the coil S.

Experiment three

In the third experiment, he discovered that when the coil is drawn towards the magnetic flux, the coil connected to it shrinks, implying that the coil's area within the magnetic field shrinks. When the induced current is delivered in the same direction as the coil's motion, Lenz law states that the coil's motion is opposed.

The magnet in the loop exerts a force on the current to produce it. The current must exert a force on the magnet to counteract the change.

Also check-

• NCERT Exemplar Class 11th Physics Solutions
• NCERT Exemplar Class 12th Physics Solutions
• NCERT Exemplar Solutions for All Subjects