🔍 Key Concepts

• Shunt-wound DC motor characteristics when running with no mechanical load • What happens to speed and armature current if the field current suddenly drops to zero or near zero • Relationship between field flux and motor speed/induced EMF in DC motors

💭 Think About

• Think about how motor speed depends on the strength of the magnetic field (flux) in a shunt-wound DC motor • If the field circuit opens, what happens to the flux, and how must the speed change to keep the motor’s internal voltage (back EMF) in balance with the supply voltage? • Consider whether a loss of field will tend to slow the motor down, stop it, or cause it to speed up, and what physical damage might result

✅ Before You Answer

• Review the approximate relationship: speed is inversely proportional to field flux for a DC motor under light load • Consider what happens to the armature current and mechanical speed immediately after the field opens at no load • Ask: would an opened field circuit directly cause current to increase in the field, or in the armature, or neither? And which part would be at risk of damage?