Transformer Objective Type Question Answers

21. Two things which are same for primary and secondary of transformer are 

(i) ampere-turns and voltage per turn
(ii) resistances and leakage reactances
(iii) currents and induced voltages
(iv) none of the above

22. A transformer operates poorly at very low frequencies because 

(i) permeability of core is increased
(ii) magnetising current is abnormally high
(iii) primary reactance is too much increased
(iv) none of the above

23. If a power transformer is operated at very high frequencies then 

(i) primary reactance is too much increased
(ii) primary will draw large power
(iii) core losses will be excessive
(iv) none of the above

24. The primary leakage flax links  

(i) primary winding only
(ii) secondary winding only
(iii) both primary and secondary windings
(iv) none of the above

25. The effect of leakage flux in a transformer is to ……. ……..

(i) increase copper losses
(ii) decrease copper losses
(iii) cause voltage drop in the windings
(iv) none of the above

26. Leakage flux iu a transformer occurs because 

(i) iron core has high permeability
(ii) air is not a good magnetic insulator
(iii) applied voltage is sinusoidal
(iv) transformer is not an efficient device

27. The mutual flux in a transformer remains constant at all loads because

(i) applied voltage and frequency are constant
(ii) leakage flux is small
(iii) iron core is used
(iv) losses are small

28. Fig. 2 shows an actual transformer on load. The currents I’₂ and I₂ will be 

(i) in phase
(ii) 180° out of phase
(iii) 90° out of phase
(iv) none of the above

29. The relation between primary ampere-turns and secondary ampere-turns in Fig. 2 is  

(i) N₁I’₂ = N₂I₂
(ii) N₁I₁ = N₂I₂
(iii) N₁I_o = N₂I₂
(iv) none of the above

30. The relation between I‘₂ and I₂ in Fig. 2 is 

(i) I’₂ = (N₁/N₂)I₂
(ii) I’₂ = (N₂/N₁)I₂
(iii) I’₂ = (N₂/N₁)²I₂
(iv) I’₂ = (N₁/N₂)²I₂

31. If N₂/N₁ = 0.1 in Fig. 2 and I₂ = 500 A, then I₁, is nearly equal to

(i) 5000 A
(ii) 50 A
(iii) 5 A
(iv) none of the above

32. Referring to the approximate equivalent circuit of an actual transformer on load in Fig. 3, the secondary resistance R₂ when transferred to primary becomes 

(i) (N₁/N₂)²R₂
(ii) (N₂/N₁)²R₂
(iii) (N₁/N₂)R₂
(iv) (N₂/N₁)R₂

33. Referring to Fig. 3, the secondary leakage reactance X₂ when transferred to primary becomes  

(i) (N₁/N₂)X₂
(ii) (N₂/N₁)X₂
(iii) (N₂/N₁)²X₂
(iv) (N₁/N₂)²X₂

34. Referring to Fig 3, we have . .

(i) I₁N₁ = I₂N₂
(ii) I₂’N₁ = I₂N₂
(iii) I₁N₂ = I₂N₁
(iv) none of the above

35. Referring to Fig 3, the secondary load voltage V₂ when transferred to primary becomes 

(i) (N₁/N₂)²V₂
(ii) (N₂/N₁)²V₂
(iii) (N₁/N₂)V₂
(iv) (N₂/N₁)V₂

36. Referring to Fig. 3, if V₁ = 100 V, I_w = 3 A and I_m = 4 A, then, I_o will be

(i) 7 A
(ii) 1 A
(iii) 5 A
(iv) none of the above

37. For the values given in the above question, the iron loss in the transformer will be  

(i) 300 W
(ii) 500 W
(iii) 400 W
(iv) none of the above

38. In Fig. 4, the primary will see an impedance of 

(i) 20 Ω
(ii) 100 Ω
(iii) 1.25 Ω
(iv) none of the above

39. The primary current I_p in Fig. 4 will be

(i) 46 A
(ii) 23 A
(iii) 2.3 A
(iv) none of the above

40. The secondary current I_s in Fig. 4 will be 

(i) 11.5A
(ii) 46A
(iii) 23 A
(iv) none of the above