Question
(a) A 200-turn circular loop of radius 50.0 cm is vertical, with its axis on an east-west line. A current of 100 A circulates clockwise in the loop when viewed from the east. The Earth’s field here is due north, parallel to the ground, with a strength of $3.00\times 10^{-5}\textrm{ T}$ . What are the direction and magnitude of the torque on the loop? (b) Does this device have any practical applications as a motor?
1. $0.471\textrm{ N}\cdot\textrm{m}$, clockwise when viewed from above.
2. Whether this motor has practical applications depends on how the loop is connected to the source of the current. The curent needs to always be clockwise when viewed from the East, which requires the contacts to switch polarity every half rotation. The question doesn't tell us if this is the case. Without this kind of connection, the loop will oscillate back and forth, which limits its practical applications.

# OpenStax College Physics, Chapter 22, Problem 48 (Problems & Exercises)

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