🔍 Key Concepts
• Shunt-wound DC motor basics – armature is in parallel with the field winding
• Effect of added resistance in the armature circuit on voltage to the armature and motor speed
• Effect of added resistance in the field circuit on field current, field strength (flux), and its impact on speed
💭 Think About
• For armature control: If you add resistance in series with the armature, what happens to the voltage across the armature and the torque/speed?
• For field control: In a shunt motor, if you increase resistance in the field circuit, what happens to field current, magnetic flux, and then to the speed?
• Compare: Does a weaker magnetic field tend to make a shunt motor run faster or slower, assuming load stays about the same?
✅ Before You Answer
• Be clear that in armature rheostat control, the added resistance is in series with the armature, not the field.
• Be clear that in field rheostat control, the added resistance is in series with the shunt field winding, changing field current and flux, not armature current directly.
• Before picking a choice, verify you have opposite effects for changing resistance in the armature circuit versus the field circuit for a shunt motor.