उत्तर : 3. "कैपेसिटर मोटर"
व्याख्या :

Cylindrical rotors are used in high-speed alternators having speed between 1500 rpm to 3000 rpm and salient pole rotors are used in low-speed devices, from 100 rpm to 1500 rpm. Cylindrical type rotors are used in turbo-alternators and these are made up of solid steel forging to get high mechanical stress.