Question 1
A round flat metal coil has 180 turns and negligible resistance. It is connected in a series circuit with a
resistor, with nothing else in the circuit. You measure that a
current flows through the resistor when a magnetic field through the coil, perpendicular to its area, is changing at
What is the radius of the coil?
◦ 0.54 m
◦ 0.25 m
◦ 0.014 m
◦ 0.043 m
Question 2
A long vertical wire carries a steady 70 A current. As shown in the figure, a pair of horizontal rails are 0.20 m apart. A 20-Ω resistor connects points
a and
b, at the end of the rails. A bar is in contact with the rails, and is moved by an external force with a constant horizontal velocity of 0.90 m/s to the right, as shown. The bar and the rails have negligible resistance. At the instant that the bar is 0.20 m from the wire, what are the induced current in the resistor and its direction through the resistor? (
μ0 = 4π × 10
-7 T ∙ m/A)
◦ 0.63 μA, from
a to
b◦ 0.32 μA, from
a to
b◦ 0.32 μA, from
b to
a◦ 0.63 μA, from
b to
a◦ 1.9 μA, from
b to
a
long bone
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