Review Questions

13.1 Refer to the two magnetically coupled coils of Fig. 13.69(a). The polarity of the mutual voltage is:

(a) Positive (b) Negative

Figure 13.69

For Review Questions 13.1 and 13.2.

13.2 For the two magnetically coupled coils of Fig. 13.69(b), the polarity of the mutual voltage is:

(a) Positive (b) Negative

13.3 The coefficient of coupling for two coils having L1 = 2 H, L2 = 8 H, M = 3 H is:

(a) 0.1875	(b) 0.75
(c) 1.333	(d) 5.333

13.4 A transformer is used in stepping down or stepping up:
- (a) dc voltages (b) ac voltages (c) both dc and ac voltages
13.5 The ideal transformer in Fig. 13.70(a) has N2∕N¹ = 10. The ratio V2∕V1 is:

(a) 10 (b) 0.1 (c) −0.1 (d) −10

Figure 13.70 For Review Questions 13.5 and 13.6.

13.6 For the ideal transformer in Fig. 13.70(b), N2∕N1 = 10. The ratio i2∕I1 is:
- (a) 10 (b) 0.1 (c) −0.1 (d) −10
13.7 A three-winding transformer is connected as portrayed in Fig. 13.71(a). The value of the output voltage Vo is:

(a) 10 (b) 6 (c) −6 (d) −10

For Review Questions 13.7 and 13.8.

13.8 If the three-winding transformer is connected as in Fig. 13.71(b), the value of the output voltage Vo is: (a) 10 (b) 6 (c) −6 (d) −10
13.9 In order to match a source with internal impedance of 500 Ω to a 15-Ω load, what is needed is:
- (a) step-up linear transformer
- (b) step-down linear transformer
- (c) step-up ideal transformer
- (d) step-down ideal transformer
- (e) autotransformer
13.10 Which of these transformers can be used as an isolation device?
- (a) linear transformer (b) ideal transformer (c) autotransformer (d) all of the above

Answers: 13.1b, 13.2a, 13.3b, 13.4b, 13.5d, 13.6b, 13.7c, 13.8a, 13.9d, 13.10b.