# MCQs on Electrical Machines 5

1. The rotor of a stepper motor has

Under construction.

2. The electric motor used in domestic mixers is

Under construction.

3. A 3 -Φ induction motor has a starting torque of 100 % and a maximum torque of 200 % of full load torque. Find the slip at maximum torque?

Tst = Tf and Tmax = 2Tf . So Tst / Tmax = 2a / a2 + 1 = ½
⇒ a2 - 4a + 1 = 0
⇒ a = 0.268 ( rejecting higher value).
Slip at maximum torque a = 0.268 = 26.8 %.

4. Linear induction motor is used in which purpose?

Under construction.

5. In the network shown in the figure, if voltage V at the time considered is 20 V, then dV / dt at that time will be?

V = 20 V, Current through the 20 ohm resistor is 20 / 20 = 1 amp. Voltage across 10 ohm resistor = 40 - 20 = 20 V. So current through capacitor = 2 - 1 = 1 amp. Therefore C × dV / dt = ( 1 / 2 ) dV / dt = 1 amp, so dV / dt = 2 V / s.

6. Neglecting all losses, the developed torque T of a d.c separately excited motor, operating under constant terminal voltage, is related to its output power P as

Under construction.

7. A 4 pole generator with 16 coil has a two layer lap winding. The pole pitch is

Under construction.

8. If the speed of a dc motor increases with load torque, then it is a

Under construction.

9. Crawling in an IM is due to

Under construction.

10. Emf induced in the rotor of 3 -Φ IM is proportional to the

Under construction.

11. If two mechanically coupled alternators deliver power at 50 Hz and 60 Hz respectively, then highest speed of the alternators is

Under construction.

12. Type of fuel used and moderator in Magnox reactor in nuclear plant are

As coolant here we use CO2.

13. Slip in an IM can be measured by which of these methods?

Under construction.

14. What are the methods we use to find voltage regulation of an alternator?

Under construction.

15. Which of the prime mover is least efficient?

Under construction.

16. One of the super thermal power station is located at

Under construction.

17. Torque of an induction motor varies with voltage as

Under construction.

18. The draught which a chimney produces is called

Under construction.

19. _________ is a closed loop system

Under construction.

20. The gain of an opamp is maximum at

Under construction.