21. A transformer having 100 turns of primary side is applied with 200 V ac. In order to get 400 V ac on secondary side the number of turns on the secondary side must be
a. 200
b. 800
c. 50
d. 100
22. Which of the following transformer will be largest insize
a. 1 KVA, 25 Hz
b. 1 KVA, 50 Hz
c. 1 KVA, 60 Hz
d. 1 KVA, 100 Hz
23. A step up transformer increases
a. power
b. power factor
c. voltage
d. frequency
24. In a step down transformer
a. secondary turns are less than primary
b. secondary power is less than primary power
c. phase shift is always 180
d. secondary current is always more than primary current
25. A transformer has a full load iron loss of 900 W and copper loss of 1600 W. At what percent of the load . the transformer will have maximum efficiency?
a. 100%
b. 90%
c. 75%
d. 50%
26. Power transformers are usually designed to have maximum efficiency
a. near full load
b. at 75% of full load
c. at 50% of full load
d. between 50% and 75% of full load
27. Distribution transformers are usually designed to have maximum efficiency
a. near full load
b. near 75% of full load
c. near 50% of full load
d. near no load
28. Iron losses of a transformer can be approximately calculated if
a. the guage of sheet used in core is 39 known
b. the material of core and yoke is known
c. the weight of core and yoke is known
d. the shape of core and yoke is known
29. In high frequency transformers
a. carbon cores are used
b. wooden cores are used
c. ferrite cores are used
d. aluminium cores are used
30. Total losses at full load are
a. 104.4 KW
b. 48 KW
c. 52.2 KVA
d. 26.1 KVA
