The correct answer is: The motor will not work and come to stop.
A differentially compounded DC motor has two field windings, a series field and a shunt field. The series field is connected in series with the armature, while the shunt field is connected in parallel with the armature. The series field provides the torque that drives the motor, while the shunt field provides the speed regulation.
If the shunt field suddenly opens, the motor will lose its speed regulation. The motor will continue to run, but it will run at a much higher speed than it was designed to run. This is because the series field will now be the only field winding that is providing any torque. The series field is much stronger than the shunt field, so the motor will run at a very high speed.
The high speed of the motor will cause the armature to overheat. The armature windings will start to melt, and the motor will eventually come to a stop.
Here is a brief explanation of each option:
- Option A: The motor will first stop and then run in opposite direction as series motor. This is not possible. The motor will not stop, and it will not run in the opposite direction.
- Option B: The motor will work as series motor and run at slow speed in the same direction. This is also not possible. The motor will not work as a series motor, and it will not run at a slow speed.
- Option C: The motor will work as series motor and run at high speed in the same direction. This is possible, but it is not the most likely outcome. The most likely outcome is that the motor will not work and come to a stop.
- Option D: The motor will not work and come to stop. This is the most likely outcome. If the shunt field suddenly opens, the motor will lose its speed regulation and will eventually come to a stop.