How Lenz’s Law Relates to the Conservation of Energy

The law of conservation of energy and Lenz’s law are closely related to each other. The conservation of energy involves the application of Lenz’s law. It states that energy cannot be created or destroyed, but it can be converted into another form.

According to Lenz’s law, the direction of the current opposes the magnetic flux’s change. You need extra effort to overcome the opposing forces. An increase in magnetic flux results in increasing induced current. So, the extra effort gets converted into electrical energy, which can be viewed as the law of conservation of energy.

Lenz’s Law

According to Lenz’s law, the induced current in a circuit runs opposite to the change in magnetic flux. This theory was formulated in 1834 by the German physicist Emil Lenz. 

The law specifies the direction of induced current, but it does not specify the magnitude of the current. An induced current flow connected to the closed circuit generates a magnetic flux opposite to the initial magnetic flux. This is due to the magnetic flux’s connection to the circuit. In closed circuits, induced current flows are reduced by the magnetic flux in such a way that magnetic flux is produced in the opposite direction.

The formula of Lenz’s law is represented as

E = – N (dΦ/dt)

The negative sign in the above equation indicates that the induced current in a circuit runs opposite to the change in magnetic flux.

Situation 1

When a bar magnet’s north pole is moved towards the coil, the induced current flows counterclockwise when viewed from the coil side. This creates a north polarity on the coil. The same poles repel each other, so the north pole repels the north pole. This means that it opposes the motion of a north pole magnet. 

As a result, the magnet’s movement increases the flux through the coil, while the induced current generates flux in the opposite direction.

Situation 2

When a bar magnet’s North Pole is taken away from a coil, when viewed from the coil side, the induced current flows clockwise. This creates a south polarity on the coil. Opposite poles attract each other, so the north pole attracts the south pole. This means that it opposes the motion of a north pole magnet. 

As a result, the magnet’s movement decreases the flux through the coil, while the induced current generates flux in the same direction.

Now, let us see how Lenz’s Law relates to the law of conservation of energy.

Conservation of Energy and Lenz’s Law

Conservation of energy and Lenz’s law are closely related to each other. According to Lenz’s law, the direction of the current opposes the magnetic flux’s change. Extra effort is needed to overcome the opposing forces. An increase in magnetic flux results in increasing induced current due to this additional work. The extra effort is converted into electrical energy, which can be viewed as the law of conservation of energy.

Our previous study showed that as the north pole of a magnet approaches a coil, the magnetic flux increases and decreases as it is driven away. In the first situation, the magnet is moved to oppose the cause, and the side facing the coil becomes north polarised. The north poles of the magnet and coil repel each other. Magnets and coils must be brought together mechanically to counteract the force of repulsion. Once they are brought together, mechanical energy is converted into electrical energy. As per Joule’s Effect, this electrical energy becomes heat energy.

The coil’s nearer face will become south polarised when the magnet is moved away from the coil. The electromotive force (EMF) produced by this magnet will oppose its outward motion. To defeat the force of attraction between the south pole of the coil and the north pole of the magnet, more mechanical work must be done. The mechanical work is converted into electrical energy.

In the absence of the magnet’s movement, no mechanical work is done. Thus, no EMF is produced in the coil. Therefore, Lenz’s law complies with the law of conservation of energy.

Applications of Lenz’s Law

The application of Lenz’s law in physics is as follows:

• This law shows that the induced electromotive force and the flux change have opposite signs and provides a physical interpretation of the sign selection in Faraday’s induction method.

• To see where Lenz’s Law is used in physics, we need to take a look at the metal detectors and braking system of the train along with the microphones and card readers.

• The application of Lenz’s law in physics can also be seen in the form of Eddy’s current dynamometers.

• Lenz’s law also applies to generators. When a current is induced in the generator, the direction of this induced current is to rotate the generator against the generator. Therefore, the generator requires more mechanical energy. 

• Lenz’s law is also used in electromagnetic brakes and inductive cooktops.

• Lenz’s law can also be seen in AC generators and electric generators.

Conclusion

Lenz’s law helps us understand the concept of magnetic energy stored in inductors. Conservation of energy and Lenz’s law are closely related to each other. According to Lenz’s law, the direction of the current opposes the magnetic flux’s change. Extra effort is needed to overcome the opposing forces. An increase in magnetic flux results in increasing induced current due to this additional work. The extra effort is converted into electrical energy, which is the law of conservation of energy.