🔍 Key Concepts

• Difference between mechanical input (prime mover) and electrical/magnetic excitation in a generator • Role of residual magnetism in starting voltage buildup • What actually causes the shaft to rotate in an AC generator system

💭 Think About

• Ask yourself: which option directly supplies the mechanical turning force to the generator shaft, rather than just helping produce voltage? • Consider the normal power flow: does electricity create the rotation, or does rotation create the electricity in a generator? • Think about real-world examples (diesel engine–driven generator, turbine–driven generator): what physically spins the rotor?

✅ Before You Answer

• Identify which choice describes a mechanical driving source, not a magnetic or electrical condition inside the generator • Separate in your mind: producing torque vs producing voltage – they are not the same thing • Verify which options are about the internal magnetism/electrical excitation and which is about the external machine that turns the generator