Answer
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Work Step by Step
The effect is due to eddy current braking. As discussed in section 20-6 on page 600, the external magnetic field interacts with the mobile conduction electrons in the swinging bar to cause a braking effect.
See figure 21–20. As the bar enters or leaves the magnetic field, eddy currents are created in the bar. The magnetic force on these induced currents opposes the original motion that caused the eddy currents. Thus a resistive force is felt by the bar, no matter what its direction of swing. The oscillations are quickly damped out.
