A flat coil of wire, consisting of 20 circular loops, with a total resistance of

Question

A flat coil of wire, consisting of 20 circular loops, with a total resistance of 20.0 ohms, is placed so that it is at rest, flat on a table. The graphs above show the magnetic flux through each loop of the coil as a function of time, for three different cases. The units of flux are webers, which are equivalent to tesla meters2. The flux through each loop changes because the magnetic field changes . Assume that the field is uniform and the direction of the field is perpendicular to the plane of the coil - positive flux means the field is passing in one direction through the coil, and negative flux means that the field is passing through the coil in the opposite direction.



(b) Consider case A only. At t = 8 s, the induced current is directed clockwise. At which other times, for case A, is the induced current also directed clockwise. Select all that apply?
t = 2 s
t = 6 s
t = 12 s
t = 22 s

Explanation / Answer

Hi,
According to Faraday law of induction the induced electromotive force (EMF) in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit.
At case A at 8th second we have positive change at flux (flux became bigger with a time), then we will have current at the same direction in all other times when the flux change is positive.
According to graph A this will happen only between second 20 to 25.
therefore the right answer is t=22 sec

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