Lenz's Law and Conservation of Energy: Overview, Questions, Preparation

Lenzs law is like a referee in the flux game. According to this law, The induced current should always be in a direction which opposes it’s cause i.e. change in the magnetic flux. Magnetic flux can be defined by the general formula:

B⋅A⋅cosθ

Where,

• θ = angle between the normal and magnetic flux
• A = Surface Area

Lenz law introduces a negative sign into the faraday second law of electromagnetic induction in order to define the direction that should necessarily be opposite.

Mathematical Representation:

EMF​=−dϕB​/dt

Where,

• B = magnetic field
• dϕB​/dt = rate of change in magnetic flux
• “-“= negative sign (according to lenz law)

Let us imagine a magnet moving towards a coil. As the magnet gets closer, the magnetic flux increases through the coil. The coil will repel this increase in the magnetic flux by introducing it’s own magnetic field in the opposite direction. This opposition will lead to generation of electric current in the whole coil.

Now, suppose we move the magnet away from this circuit. Now, the magnetic flux will start to decrease in the coil. The coil will now generate an electric current in the same direction with the aim of opposing this pulling back of the magnet. Now, the current will move in the opposite direction. This opposition was an indication of the coil’s resistance to change which led to the generation of current.

This is how the circuit works!

Here are a few important reasons why this law is considered as the foundation principle for electromagnetism:

1. Lenz law heavily depends on the principle of conservation of energy. The work done in moving the magnet (mechanical energy) is converted into electrical energy. This electrical energy is opposed by the magnetic field, which in turn ensures that the energy gets conserved.
2. This law is an extremely crucial factor in determining the direction of the induced current through the negative sign. By understanding the magnetic flow of the circuit, we can easily predict the exact direction in which the current can be expected to flow.
3. Principles used in this law are used in designing of various modern day electrical appliances used in our daily lives such as electric heaters, induction motors, generators, cookers, transformers, power plants etc. All these devices are invented using the principles of electromagnetic induction.
4. Faraday laws of electromagnetic induction and Lenz Law of electromagnetic induction are directly connected to each other, and these laws combined together were used to introduce a new way of generating electricity from magnetic field, which turned out to be a revolutionary step for the field of physics.