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


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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