We have two coils placed close to each other. When we switch on the battery connected to primary coil while keeping the sliding contact of rheostat at fixed position, the reading of Galvanometer:
Correct answer: A. First increases and then becomes zero
- A. First increases and then becomes zero
- B. First increases and then becomes constant at some value
- C. Increases with the passage of time
- D. Remains zero
Explanation
Explanation:At that instant when the switch is closed momentarily current flows through the secondary coil due to change in magnetic flux. Galvanometer shows deflection after that the further flux will change so current in secondary will be zero. This option is not correct because the current induced in the secondary coil is not sustained, and therefore, the galvanometer reading cannot remain constant. This option is also incorrect because the current induced in the secondary coil decays with time due to the resistance of the circuit, and therefore, the galvanometer reading cannot increase with time. This option is also incorrect because a momentary current is induced in the secondary coil due to mutual induction, and this current causes a momentary deflection in the galvanometer. Therefore, the galvanometer reading cannot remain zero.
This question appeared on the UHS MDCAT 2009 paper, which you can sit online with every answer explained.
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About Faraday's Law
Faraday's law states that an induced electromotive force equals the rate of change of magnetic flux linkage through a circuit. Questions cover changing field, area, angle or motion, the negative sign associated with Lenz's law, and the distinction between induced emf and the current that may flow in a closed circuit.
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