Question

Define Lenz's law.

Hint:

Think of Lenz's Law as the physical embodiment of resistance to change. The induced current acts like a stubborn system: if you try to increase the magnetic field, it creates a field to oppose the increase; if you try to decrease it, it creates a field to maintain it.

Answer 1

Step 1: Scientific Statement:
Lenz's Law states that the direction of an electromagnetically induced electromotive force (emf) or current will always be such that it produces physical or magnetic effects that directly oppose the change in magnetic flux that caused it.

Step 2: Mathematical Expression:
Faraday's Law of Electromagnetic Induction is mathematically expressed as: $$e = -N \frac{d\Phi}{dt}$$ Where:

• $e$ is the induced electromotive force (emf) (in Volts).
• $N$ is the number of turns in the winding.
• $\frac{d\Phi}{dt}$ is the rate of change of magnetic flux (in Weber/second).

The negative sign ($-$) represents Lenz's Law, indicating opposition to the change in magnetic flux.

Step 3: Relation to Conservation of Energy:
Lenz's Law is a direct consequence of the Law of Conservation of Energy. To generate electrical power (induced current), mechanical work must be performed against the opposing magnetic forces created by the induced current. If the sign were positive, it would lead to an infinite feedback loop of energy generation without any input, which violates physical laws.