Differences Between Lenz’s Law And Faraday’s Law

While Faraday’s law tells us the magnitude of the EMF produced, Lenz’s law tells us the direction that current will flow. Lenz’s Law is not quantitative, but it can be used when Faraday’s Law of Induction cannot be used. 

How are Faraday’s Law and Lenz’s Law related?

Faraday’s Law says when the magnetic flux is linked with the conductor changes, EMF is induced in the conductor: 

 Ɛ=dΦdt

 ‘Φ’ stands for magnetic flux. 

The negative sign in the previous equation shows that the induced EMF’s direction opposes the cause that created it, which is the expression of Lenz’s Law.

Thus, Lenz’s Law says that as per Faraday’s Law, whenever EMF is induced, its direction always is the opposite the change in flux which produced it, giving us the magnitude of the induced EMF. 

What are Faraday’s Law and Lenz’s Law?

Here’s a quick introduction to both the laws: 

 Faraday’s Law:

Faraday’s Law of electromagnetic induction completes the link between electric circuits and a magnetic field by explaining their relation through this Law, which is considered the working principle behind most electrical motors, inductors, etc., generators.

Faraday’s First Law:

According to Faraday’s First Law, an induced EMF is found across the conductor whenever a conductor is placed in a varying magnetic field. When the conductor is a closed circuit, the induced current flows through it.

Various methods exist for varying the magnetic field:

1. Using a magnet that moves

2. By adjusting the coil

3. Rotating the coil with the magnetic field

Faraday’s Second Law:

Faraday has two laws. Faraday’s Second Law says that the amplitude of the induced EMF always matches the rate of change of the flux associated with the source during electromagnetic induction.

The flux linkages are generally the product of several turns and the flux associated with the coil.

Formula Of Faraday’s Second Law:

Whenever we consider the conductor is moving in the magnetic field, then the amount of flux linked with the coil at the initial position of the conductor = NΦ₁ (Wb) 

(N = speed of the motor and Φ = flux)

• flux linked with the coil at the final position of the conductor = NΦ₂ (Wb)

Hence the change in the number of flux linked = N(Φ₁ – Φ₂)

And let, Φ₁ – Φ₂ = Φ,

• therefore, the change in the flux can be written as = NΦ

and the rate of change of flux linkage is given by NΦ/t

taking the derivative of RHS

rate of change of flux linkages is found to be = N (dΦ/dt)

by Faraday’s Law of electromagnetic induction, the rate of change of flux linkages equals the induced EMF

So, E = N (dΦ/dt) (volts)

Lenz’s Law:

Lenz’s Law of electromagnetic induction says that as per Faraday’s Law, whenever EMF is induced, its direction always is the opposite. 

Taking Lenz’s Law into account,

E is equal to -N (d/dt) (volts)

The negative sign states that both the direction of change and induced EMF in magnetic fields have opposite signs.

Lenz Law v/s Faraday’s Laws; the differences:

According to Faraday’s and Lenz’s laws of electromagnetic induction, any magnetic field formed by an induced current will be in the opposite direction as the original field’s change, with the following exceptions:

 Conclusion:

This article studied Faraday’s Law and Lenz’s Law and the relationship between electromotive force and Faraday’s law in Lenz’s law. 

Faraday, in his law, has often used Lenz’s Law as a negative sign before the derivatives. The negative sign reminds us that the EMF is pointing toward resisting the flux change. (If the EMF were to enforce the flux change, we would get a runaway condition that would be completely unstable and violate the principle of energy conservation.)