An a.c. generator can be converted to a d.c. electric motor by replacing the

Analyze the question: We are asked how to convert an a.c. generator into a d.c. motor. We need to compare the parts of the two machines.

Concept:

• An a.c. generator (alternator) has slip rings. They carry the alternating current from the rotating coil to the external circuit without reversing it.
• A d.c. motor has a split-ring commutator. It reverses the current in the coil every half turn, so the torque always acts in the same direction and the coil keeps rotating one way.
• A motor needs an electrical input. A generator needs a mechanical input (turning the coil) and gives out electrical energy.

Step-by-step solution:

1. The a.c. generator's slip rings would make the force on the coil's sides reverse every half turn. The coil would just oscillate and not rotate continuously. So the slip rings must be replaced.
2. Replace the slip rings with a split ring (commutator). This keeps the torque in one direction.
3. Connect a battery (d.c. source) to supply current to the coil through the brushes. The coil then sits in the magnetic field and experiences a force (motor effect, Fleming's left-hand rule).

Checking the options:

• A. Slip rings replaced with a split ring and a battery connected. This is correct.
• B. This is the reverse. It would turn a motor into a generator, not the other way round.
• C and D. These are badly worded. You cannot replace "a.c." with "d.c." as a component, and C keeps the slip rings, which would not give continuous rotation.

Answer: A

Tip: Remember "Slip rings → a.c. generator; Split ring → d.c. motor." For a motor, think "split ring + battery in". For a generator, think "turn the coil to get current out".