Question

Which of the following laws gives the direction of induced emf?
A. Lenz’s law
B. Fleming left hand rule
C. Ohm’s law
D. Faraday’s law of electromagnetic induction

Answer 1

Hint: In order to solve this question, we will examine each option one by one with their standard definitions and then will check which law among the given options gives the direction of induced emf. EMF stands for Electromotive force which is none other than potential development across the conductor when placed in changing magnetic flux.

Complete answer:
Faraday’s law of electromagnetic induction states that due to change in magnetic flux per unit time an emf would be induced in a loop which in turn induces current in the loop. Magnetic flux could be changed in three different ways, first is by changing magnetic field with time, second by reducing or increasing the loop under constant magnetic field and third one is by changing orientation of loop in magnetic field.

Lenz’s law stating current direction is in such a way that it opposes the cause of its generation so from this law emf induced direction would be decided. The direction of current will be such that it opposes the increasing or decreasing magnetic flux passing through it.Fleming left hand rule signifies the relation between direction of magnetic field, current induced and motion of conductor. According to which all three are perpendicular to each other.

 If we stretch the thumb, middle finger and index finger such that they are perpendicular to each other. Then if the thumb points in the direction of motion of the conductor and the index finger denotes the direction of the magnetic field then the middle finger would point out in the direction of induced current.

So the correct answer is A.

Note: It should be remembered that Lenz’s law and Fleming left hand rule both denote the direction of current but Lenz’s law is in general more efficient because Fleming’s left hand rule is applicable only when the induced emf is due to motion of conductor. While Ohm’s law is merely the relation between voltage and current in a conductor.