Question

The polarity of induced emf is given by

• A. Ampere’s circuital law
• B. Biot-Savart law
• C. Lenz’ law
• D. Fleming’s right hand rule
• E. Fleming’s left hand rule

Hint:

Think of Lenz's law as the "Newton's Third Law" or "Le Chatelier's Principle" of electromagnetism—nature always tries to oppose the change being forced upon it!

Answer 1

The Correct Option is C

Concept: Electromagnetic induction is the process where a changing magnetic flux through a circuit induces an electromotive force (EMF).
• Faraday's Law: States that the magnitude of the induced EMF is equal to the rate of change of magnetic flux.
• Lenz's Law: Provides the direction (polarity) of this induced EMF. It states that the direction of the induced current is such that it creates a magnetic field which opposes the change in magnetic flux that produced it.

Step 1: Identify the law governing polarity.
The question specifically asks for the "polarity," which refers to the direction of the induced EMF. According to Lenz's law, the negative sign in Faraday's equation (\( \epsilon = - \frac{d\Phi}{dt} \)) represents this opposition.

Step 2: Differentiate from other electromagnetic laws.

• Ampere's and Biot-Savart laws: Relate electric currents to the magnetic fields they produce.
• Fleming's rules: Relate the directions of force, magnetic field, and current, but Lenz's law is the fundamental principle used to determine the polarity of induced EMF caused by flux changes.