Question

State whether True or False: Lenz’s law defines the polarity of the induced voltage.
(A) True
(B) False

Answer 1

Hint: Lenz’s law in magnetism is used to find the direction of induced emf (electromotive force) and current. It is based on the law of energy conservation which has plenty of applications like –
a) AC generator
b) Metal detector
c) Braking system of train
d) Microphones

Complete step by step answer:
According to Faraday’s equations of electromagnetic induction, the negative sign indicates the direction of induced current driven by the induced emf around a circuit. However, the same direction for induced current can be easily determined with the help of Lenz’s law. Lenz’s law states that: - The direction of the magnetic induction effect is such as to oppose the cause of the effect.

Figure1 showing a bar magnet is allowed to move vertically upward away from the coil so, according to Lenz’s law the induced current I will be circulated in a clockwise direction to generate induced magnetic fields in the same direction as shown in the above figure. This suggests that induced magnetic flux is actually supporting the previous flux and opposes the change which produces it while in the case of figure 2. a bar magnet is allowed to fall vertically downward toward the coil as a result the magnetic field lines passing through the coil in a downward direction increases so, according to Lenz’s law the induced current I will be circulated in the anticlockwise direction to generate induced magnetic field in the opposite direction to oppose the change.

Hence, Option (A) is the correct answer.

Note: Students should keep the points that make the difference between Lenz’s law and Faraday’s law. Lenz’s law is based on the law of energy conservation whereas Faraday’s law is about the electromagnetic force produced. Lenz’s law is used to determine the direction of induced emf the negative sign indicates that the direction induced emf in the coil is in the opposite direction of the magnetic flux linked with the coil.