Answer
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Work Step by Step
First see Figure 21–14. The induced current labeled “a” points into the page. It sits in a magnetic field that points from left to right. Use a right-hand rule to find the force on a current-carrying wire, with the current going into the page and the magnetic field pointed to the right. The force is downward, which corresponds to a counterclockwise torque (the torque vector is out of the page). As we can see, this counter torque opposes the clockwise motion of the generator.
The induced current labeled “b” points out of the page. It sits in a magnetic field that points from left to right. Use a right-hand rule to find the force on a current-carrying wire, with the current coming out of the page and the magnetic field pointed to the right. The force is upward, which corresponds to a counterclockwise torque (the torque vector is out of the page). As we can see, this counter torque opposes the clockwise motion of the generator.
Next, see Figure 21–17. The induced current from point “a” to point “b” is directed into the page. It sits in a magnetic field that points from left to right. Use a right-hand rule to find the force on a current-carrying wire, with the current going into the page and the magnetic field pointed to the right. The force is downward, which corresponds to a counterclockwise torque (the torque vector is out of the page). As we can see, this counter torque opposes the clockwise motion of the generator.
Now consider the induced current from point “c” to point “d”, which is directed out the page. It sits in a magnetic field that points from left to right. Use a right-hand rule to find the force on a current-carrying wire, with the current coming out of the page and the magnetic field pointed to the right. The force is upward, which corresponds to a counterclockwise torque (the torque vector is out of the page). As we can see, this counter torque opposes the clockwise motion of the generator.