Motional EMF

Practice Questions:

Question 1: difficult

A metal disc rotates freely, between the poles of a magnet in the direction indicated. Brushes P and Q make contact with the edge of the disc and the metal axle.What current, if any, flows through R?

1. a current from P to Q

2. a current from Q to P

3. no current, because the emf in the disc is opposed by the back emf

4. no current, because the emf induced in one side of the disc is opposed by the emf induced in the other side.

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Question 2: difficult

A rectangular loop has a sliding connector PQ of length l and resistance RΩ and it is moving with a speed v as shown. The set-up is placed in a uniform magnetic field going into the plane of the paper. The three currents I1, I2 and I are

1. \[I_{1}=I_{2}=I=\frac{Blv}{R}\]

2. \[I_{1}=I_{2}=\frac{Blv}{6R}=I=\frac{Blv}{3R}\]

3. \[I_{1}=-I_{2}=\frac{Blv}{R}=I=\frac{2Blv}{3R}\]

4. \[I_{1}=I_{2}=\frac{Blv}{3R}=I=\frac{2Blv}{3R}\]

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Question 3: difficult

A conducting rod AC of length 4l is rotated about a point O in a uniform magnetic field \[\overrightarrow{B}\] directed into the paper. AO = l and OC = 3l. Then

1. \[V_{A}-V_{0}=\frac{B\omega l^{2}}{2}\]

2. \[V_{0}-V_{C}=\frac{9}{2}B\omega l^{2}\]

3. \[V_{A}-V_{C}=8B\omega l^{2}\]

4. \[V_{C}-V_{0}=\frac{9}{2}B\omega l^{2}\]

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