21. A single-phase full-converter is fed to a d.c. motor. The average speed of the motor is zero, when firing angle is :
(A) 0
(B) 90°
(C) 180
(D) 360°
22. As compared to constant – current system, the constant voltage system of charging a lead acid cell has the advantage of :
(A) avoiding excessive gassing
(B) increasing time of charging
(C) decreasing cell capacity of
(D) increasing the temperature
23. The primary of a transformer has twice the number of turns as the secondary. If the primary voltage is 220 V and a 5 12 resistive load is connected across the secondary, the power delivered to the load is :
(A) 9680 W
(B) 605 W
(C) 2420 W
(D) 1100 W
24. MCCB stands for :
(A) Moulded Case Circuit Breaker
(B) Main Case Circuit Breaker
(C) Moulded Current Circuit Breaker
(D) Main Current Circuit Breaker
25. Four resistances of 2Ω,4Ω, 2Ω and 8Ω are connected in parallel. The equivalent value of conductance is :
(A) 1/16℧
(B) 25/24℧
(C) 8/11℧
(D) 11/8℧