### Electrical Machines (Transformer)

1. How many primary volts must be applied to a transformer with a turns ratio of 0.1 to obtain a secondary voltage of 9 V?

A. 9 V

B. 90 V

C. 900 V

D. 0.9 V

2. In a certain loaded transformer, the secondary voltage is one-fourth the primary voltage. The secondary current is

A. one-fourth the primary current

B. four times the primary current

C. equal to the primary current

D. one-fourth the primary current and equal to the primary current

3. A certain transformer has a turns ratio of 1 and a 0.85 coefficient of coupling. When 2 V ac is applied to the primary, the secondary voltage is

A. 1.7 V

B. 0.85 V

C. 1 V

D. 0 V

4. The primary coil of a transformer is connected to a 60 V ac source. The secondary coil is connected to a 330 load. The turns ratio is 3:1. What is the secondary voltage?

A. 2 V

B. 20 V

C. 180 V

D. 18 V

5. The primary winding of a power transformer should always be

A. open

B. shorted

C. switched

D. fused

6. A certain amplifier has 600 internal resistance looking from its output. In order to provide maximum power to a 4 speaker, what turns ratio must be used in the coupling transformer?

A. 8

B. 0.8

C. 0.08

D. 80

7. A transformer

A. changes ac to dc

B. changes dc to ac

C. steps up or down dc voltages

D. steps up or down ac voltages

8. The primary of a transformer is connected to a 6 V battery. The turns ratio is 1:3 and the secondary load, RL, is 100 . The voltage across the load is

A. 0 V

B. 6 V

C. 18 V

D. 2 V

9. To step 120 V ac up to 900 V ac, the turns ratio must be

A. 75

B. 750

C. 7.5

D. 0.13

10. When a 200 load resistor is connected across the secondary winding of a transformer with a turns ratio of 4, the source "sees" a reflective load of

A. 50

B. 12.5

C. 800

D. 0

11. In a certain transformer, the input power to the primary is 120 W. If 8.5 W are lost to the winding resistance, what is the output power to the load, neglecting any other issues?

A. 0 W

B. 14.1 W

C. 111.5 W

D. 1,020 W

12. When a 6 V battery is connected across the primary of a transformer with a turns ratio of 8, the secondary voltage is

A. 0 V

B. 6 V

C. 48 V

D. 0.75 V

13. What is the coefficient of coupling for a transformer in which 4% of the total flux generated in the primary does not pass through the secondary?

A. 0.4

B. 4

C. 9.6

D. 0.96

14. A transformer has a 1:6 turns ratio and a secondary coil load resistance of 470 . The load resistance as seen by the source is

A. 1.3

B. 7.8

C. 78

D. 13

1. b

2. b

3. a

4. b

5. d

6. c

7. d

8. a

9. c

10. b

11. c

12. a

13. d

14. d

A. 9 V

B. 90 V

C. 900 V

D. 0.9 V

2. In a certain loaded transformer, the secondary voltage is one-fourth the primary voltage. The secondary current is

A. one-fourth the primary current

B. four times the primary current

C. equal to the primary current

D. one-fourth the primary current and equal to the primary current

3. A certain transformer has a turns ratio of 1 and a 0.85 coefficient of coupling. When 2 V ac is applied to the primary, the secondary voltage is

A. 1.7 V

B. 0.85 V

C. 1 V

D. 0 V

4. The primary coil of a transformer is connected to a 60 V ac source. The secondary coil is connected to a 330 load. The turns ratio is 3:1. What is the secondary voltage?

A. 2 V

B. 20 V

C. 180 V

D. 18 V

5. The primary winding of a power transformer should always be

A. open

B. shorted

C. switched

D. fused

6. A certain amplifier has 600 internal resistance looking from its output. In order to provide maximum power to a 4 speaker, what turns ratio must be used in the coupling transformer?

A. 8

B. 0.8

C. 0.08

D. 80

7. A transformer

A. changes ac to dc

B. changes dc to ac

C. steps up or down dc voltages

D. steps up or down ac voltages

8. The primary of a transformer is connected to a 6 V battery. The turns ratio is 1:3 and the secondary load, RL, is 100 . The voltage across the load is

A. 0 V

B. 6 V

C. 18 V

D. 2 V

9. To step 120 V ac up to 900 V ac, the turns ratio must be

A. 75

B. 750

C. 7.5

D. 0.13

10. When a 200 load resistor is connected across the secondary winding of a transformer with a turns ratio of 4, the source "sees" a reflective load of

A. 50

B. 12.5

C. 800

D. 0

11. In a certain transformer, the input power to the primary is 120 W. If 8.5 W are lost to the winding resistance, what is the output power to the load, neglecting any other issues?

A. 0 W

B. 14.1 W

C. 111.5 W

D. 1,020 W

12. When a 6 V battery is connected across the primary of a transformer with a turns ratio of 8, the secondary voltage is

A. 0 V

B. 6 V

C. 48 V

D. 0.75 V

13. What is the coefficient of coupling for a transformer in which 4% of the total flux generated in the primary does not pass through the secondary?

A. 0.4

B. 4

C. 9.6

D. 0.96

14. A transformer has a 1:6 turns ratio and a secondary coil load resistance of 470 . The load resistance as seen by the source is

A. 1.3

B. 7.8

C. 78

D. 13

**Answers:**1. b

2. b

3. a

4. b

5. d

6. c

7. d

8. a

9. c

10. b

11. c

12. a

13. d

14. d

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