Transformer Objective Type Question Answers

1. A transformer will work on 

(i) a.c. only
(ii) d.c. only
(iii) a.c. as well as d.c
(iv) none of the above

2. The primary and secondary of a transformer are ……… coupled.

(i) electrically
(ii) magnetically
(iii) electrically and magnetically
(iv) none of the above

3. A transformer is an efficient device because it  

(i) is a static device
(ii) uses inductive coupling
(iii) uses capacitive coupling
(iv) uses electric coupling

4. A transformer transfers electrical energy from primary to secondary usually with a change in 

(i) frequency
(ii) power
(iii) voltage
(iv) time period

5. The voltage per turn of the primary of a transformer is  …….. the voltage per turn of the secondary.

(i) more than
(ii) less than
(iii) the same as
(iv) none of the above

6. The winding of the transformer with greater number of turns will be  

(i) high-voltage winding
(ii) low-voltage winding
(iii) either high or low voltage windiny
(iv) none of the above

 

7. A transformer does not posses  ……… changing property.

(i) impedance
(ii) voltage
(iii) current
(iv) power

8. The iron-core is used to ……….. of the transformer.

(i) increase the weight
(ii) provide tight magnetic coupling
(iii) reduce core losses
(iv) none of the above

9. If a transformer core has air gaps, then

(i) reluctanue of magnetic path is decreased
(ii) hysteresis loss is decreased
(iii) magnetising current is greatly increased
(iv) eddy current is increased

10. The maximum flux produced in the core of a transformer is ………

(i) directly proportional to supply frequency
(ii) inversely proportional to supply frequency
(iii) inversely proportional to primary voltage
(iv) none of the above

11. The flux in the core of a single-phase transformer is 

(i) purely alternating one
(ii) purely rotating one
(iii) partly alternating and partly rotating
(iv) none of the above

12. A transformer is so designed that primary and secondary have 

(i) high leakage reactance
(ii) large resistance
(iii) tight magnetic coupling
(iv) good electric coupling

 13. When the primary of a transformer is connected to a d.c. supply  

(i) primary draws small current
(ii) primary leakage reactance is increased
(iii) core losses are increased
(iv) primary may bum out

14. An ideal transformer is one which

(i) has no losses and leakage reactance
(ii) does not work
(iii) has same number of primary and secondary turns
(iv) none of the above

15. A low-voltage outdoor lighting system uses a transformer that steps 120 V down to 24 V for safety. The equivalent resistance of all low-voltage lamps is 9.6 Ω. What is the current in the secondary coil ? Assume the transformer is ideal and there are no losses in the line.

(i) 2 A
(ii) 2.5 A
(iii) 4.5 A
(iv) 1.5 A

16. In the above question, what is the current in the primary coil ?

(i) 1.5A
(ii) 4.5A
(iii) 2.5 A
(iv) 0.5 A

17. In Q. 15, how much power is used ?

(i) 30 W
(ii) 20 W
(iii) 60 W
(iv) 40 W

18. Fig. 1 shows a practical transformer on no-load. The no-load current I_o

(i) is in phase with V₁
(ii) lags V₁ by 90°
(iii) lags V₁ by an angle less than 90°
(iv) leads V₁ by 90°

19. The no-load primary current I_o Fig. 1 is 

(i) wholly reactive
(ii) wholly active
(iii) partly active and partly reactive
(iv) none of the above

 

20. The no-load primary current I_o is about  ……… of full-load primary current.

(i) 3 – 5%
(ii) 15 – 30%
(iii) 30 – 40%
(iv) above 40%