Question 115Electricity & Electronics - QMED

The correct answer is D) an open field coil. An ohmmeter can be used to diagnose an open field coil in a DC motor. By measuring the resistance across the field coil terminals, the ohmmeter can detect if there is an open circuit, indicating a faulty or disconnected field coil. This is a common diagnostic test for DC motors, as an open field coil would prevent the motor from starting or running properly. The other options are not directly related to the use of an ohmmeter in diagnosing a DC motor. Synchronous speed (A) and reversed polarity (C) are not measurements that can be taken with an ohmmeter. Undercut mica (B) is a maintenance procedure for commutators, which is not the primary function of an ohmmeter in motor diagnosis.