Question

The polarity of induced emf is given by
A. Ampere’s circuital law
B. Biot-Savart’s law
C. Lenz’s law
D. Fleming’s right hand rule
F. Fleming’s Left hand rule

Answer 1

We can solve this question with the rule for finding polarity of induced emf which we can find from the part electromagnetic induction. As only 3 of the options given are regarding direction/polarity we can eliminate those which are not regarding direction. This law is based on the law of conservation of energy.

Complete answer:
As we can understand, the only 3 options regarding polarity in the options are Lenz’s law and Fleming’s rules. Fleming’s rules deal with the magnetic field and current direction, not about induced emf. So the answer is Lenz’s law
Lenz’s law: now Let’s talk about Lenz’s law.
This law is a method to find induced emf in a conducting loop. We know current is induced by change in magnetic flux. This induced current itself produces a magnetic field and hence a magnetic flex. This flux may vary in sign. If the flux have same sign it strengthens the original flux otherwise it weakens.

Lenz’s law states that “the direction of current induced is such that it opposes the change that has induced it”
As short we can say, if a current is induced by an increasing flux, it will weaken the original flux. If emf is induced by a decreasing flux, it will strengthen the actual flux.

So the correct answer is option c.

Note:
If we examine Lenz’s law deeply, we can see Lenz’s law is based upon the law of conservation of energy. As to do work opposing force, we have to put extra work which will lead to periodic change in magnetic flux and more current will be induced.so, all the extra work needed to bring the magnet through the coil will be transformed to electrical energy, i.e. emf through the coil which we can see is law of conservation of energy.