-In the figure,a wire and a 10 Ω resistor are used to form a circuit in the shape of a square, 20 cm by 20 cm.A uniform but nonsteady magnetic field is directed into the plane of the circuit.The magnitude of the magnetic field is decreased from 2.70 T to 0.90 T in a time interval of
96 ms.The average induced current and its direction through the resistor,in this time interval,are closest to:
A)75 mA,from b to a
B)45 mA,from b to a
C)75 mA,from a to b
D)45 mA,from a to b
E)110 mA,from a to b

Question

-In the figure,a wire and a 10 Ω resistor are used to form a circuit in the shape of a square, 20 cm by 20 cm.A uniform but nonsteady magnetic field is directed into the plane of the circuit.The magnitude of the magnetic field is decreased from 2.70 T to 0.90 T in a time interval of
96 ms.The average induced current and its direction through the resistor,in this time interval,are closest to:
A)75 mA,from b to a 
B)45 mA,from b to a 
C)75 mA,from a to b 
D)45 mA,from a to b 
E)110 mA,from a to b

Quizplus · Accepted Answer

The induced emf is given by:emf = -dΦ/dt = -d(BA)/dt = -B(dA/dt) = -B(20 cm)(20 cm)(1/96 ms) = -4.5 VThe average induced current is:I = emf/R = -4.5 V/10 Ω = -0.45 A = 450 mAThe direction of the induced current is given by Lenz's law, which states that the induced current will flow in a direction that opposes the change in magnetic flux. In this case, the magnetic field is decreasing, so the induced current will flow in a direction that creates a magnetic field that opposes the decreasing magnetic field. This means that the induced current will flow from b to a.

-In the Figure,a Wire and a 10 Ω Resistor Are