The three loops of wire shown in the figure are all subject to the same uniform

Question

The three loops of wire shown in the figure are all subject to the same uniform magnetic field B that does not vary with time. Loop 1 oscillates back and forth as the bob in a pendulum, loop 2 rotates about a vertical axis, and loop 3 oscillates up and down at the end of a spring. Which loop, or loops, will have an emf induced in them The long straight wire in the figure below carries a current I that is decreasing with time at a constant rate. The circular loops A, B, and C all lie in a plane containing the wire. Determine the induced emf in each of the loops A, B, and C.

Explanation / Answer

16)

The induced emf occurs when there is a change in magnetic flux. From the figure, either moving to left /right or up/down the change in flux is zero because the area is fixed and field is also fixed. So loop 1 and 3 cannot produce emf. For the second one, when the loop rotates the area that cuts the magnetic field changes from maximum to minimum or vice versa causing the change in flux to produce Induced emf.

17)

the change in the current causes change in magnetic field. The field produced above the the wire is outward changing and field below the wire is changin inward.

So the loop A will have counter clockwise emf and loop C will have clockwise emf. Here the change in field for loop B is zero as field change is zero.

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