Identify the situations in which an emf is induced. i. Two circular loops lie si

Question

Identify the situations in which an emf is induced. i. Two circular loops lie side by side in the same plane. One is connected to a source that supplies an increasing current: the other is a simple closed ring. Is there an emf induced in the ring? A long straight conductor passes through the center of a metal ring perpendicular to its plane. If the current in the conductor increases, is an emf induced in the ring? A metal rectangle is close to a long straight, current-carrying wire, with two of its sides parallel to the wire. If the current in the long wire is decreasing, is there an induced emf in the rectangle? These situations arc shown in the figure: I, ii all of them. I, iii ii none of them. i. The figure shows a conducting disk with radius R that lies in the xy-plane and rotates with constant angular velocity omega about the z-axis. The disk is in a uniform, constant B field in the z-direction. A motional emf arises because the conducting disk moves relative to B. By completing the circuit through two stationary brushes (labeled b in the figure) that make contact with the disk and its conducting shaft, we can use this device as a source of emf in a circuit, producing a current through the shaft, disk and resistor. Find the direction of the induced emf. The direction reverses from clockwise to counterclockwise and back to clockwise, with each half turn (180 degree ) of the disk. From the rim to the center of the disk. Counterclockwise around the disk. The direction reverses from clockwise to counterclockwise and back to clockwise, with each complete turn (360degree) of the disk. From the center to the rim of the disk. Clockwise around the disk.

Explanation / Answer

3. Using Lorrentz force relation of FB = e(v x B), directoin of Lorrentz force on electrons is towards the center (from the rim), hence, emf is induced in direction "from rim to the center of the disk"

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