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9 |
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When
a refrigerator/freezer compressor motor initially engages, the motor that is
powered by draws initially of current.
After a few seconds the back emf has been built up to its value of at which point the compressor motor now
draws only . What is the resistance of the motor’s
armature? |
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So the Correct Answer is C ! |
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10 |
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If
the emf induced in a circular coil exceeds the break down voltage of air,
there will be a spark of electricity across the diameter of the coil. Consider a circular coil with turns of wire around it and a radius of . An induced emf of would result in the sparking across the
coil. What is the change in magnetic
field passing through the coil that would create this sparking? |
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Solving for |
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- sign dropped as it indicates
polarity not value. |
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So Correct answer is B ! |
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11 |
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A
long straight wire has a current going to the right as shown below. What is the magnitude and direction of the
magnetic field created at a point below the wire? |
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By the right hand rule, the
direction will be into the paper (). |
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So Correct Answer is D ! |
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12 |
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As
shown above a wire is long and is carrying a current of . It is sitting in a constant external
magnetic field, which has a field strength of at an angle of . What is the magnitude and direction of the
force acting on the wire? |
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Using the right hand rule for cross
products points out of the paper .
The magnitude of the force is found by |
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So Correct Answer is B ! |
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