alleryStart learning →A motor coil rotates until the perpendicular to the loop lines up with the field. What is the torque at that instant?
AIt is twice the maximum
BIt has fallen to zero
CIt is at its maximum
DIt is half the maximum
Answer & Solution
Correct answer: B. It has fallen to zero
1. The torque is NIAB sin(theta), with theta the angle between the perpendicular to the loop and the field.
2. When that perpendicular lines up with the field, theta is zero.
3. Since sin(0) is zero, the torque falls to zero at that position.
4. The maximum torque happens a quarter turn away, where theta is 90 degrees.
_Source: OpenStax College Physics (CC BY 4.0), Ch 22 "Magnetism", section 22.8 Torque on a Current Loop: Motors and Meters_
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