Question

Assertion: In coin-operated vending machines, eddy currents are used to detect counterfeit coins, or slugs.
Reason: The coin rolls past a stationary magnet, and eddy currents slow its speed. The strength of the eddy currents, and thus the retardation, depends on the conductivity of the coin's metal.

A. Both Assertion and Reason is correct and Reason is the correct explanation of Assertion.
B. Both Assertion and Reason is correct and Reason is the not correct explanation of Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason is incorrect.

Answer 1

To check whether reason and assertion are correct or not and also whether the reason is the correct explanation of assertion or not, we will use the Faraday’s and Lenz’s law. From Faraday’s law, we can conclude that voltage will be induced because of the change in the magnetic field. Also, from Lenz’s law, we can say the current that will induce will always try to oppose the formation of the magnetic flux. Then we will check for the statements given in the question whether the statements satisfy the laws or not.

Complete step by step answer:
Eddy currents can be defined as the induction of electrical current in the form of loops inside a conductor. Eddy currents are induced because of the varying magnetic field. This induction is based on Faraday’s law of induction. According to Faraday’s law, the induced voltage depends upon the change in magnetic flux. From the conductivity of the material, we can conclude the strength of the eddy current. As in the statement, a coin-operated vending machine is used. Therefore, when the coin passes through the magnetic field, from Faraday’s law, we can conclude that eddy current will be induced in the coin. But we know from Lenz's law the induced current will oppose the motion, and the variation in the magnetic flux and hence the speed of the coin decreases. The vending machine will detect the counterfeit coins when it observes indifferent behaviour. Also, when the value of this decrement in the speed cannot be determined. As we have earlier said, the induction of current depends on the conductivity of the material.
Therefore, we can say that both assertion and reason are correct, and the reason is the correct explanation assertion.

So, the correct answer is “Option A”.

Note:
To find the answer to this question, we should have prior knowledge about Faraday’s law and Lenz's law. Since the reason is checked on the basis of Faraday’s law and the assertion is based on Lenz’s law.