Question 1

An ideal 10:1 transformer with 20 VA of power has less than 2 VA on the output.

Accepted Answer

A) True 
 B)False  False

Question 2

-In Figure 14-1, if the primary to secondary turns ratio is 7.5:1, the output voltage equals ________.

Accepted Answer

A)    
B)    
C)    
D)    
A)    
B)    
C)    
D)    B

Question 3

-When a 1   load resistor is connected across the secondary winding of a transformer with a turns ratio of 1:2, the source ʺseesʺ a reflected load of ________.

Accepted Answer

A)    
B)    
C)    
D)    
A)    
B)    
C)    
D)    D

Question 4

To couple two circuits together with no change in either voltage or current, use ________.

Accepted Answer

A) a step-down transformer 
B) a step-up transformer 
C) a power transformer 
D) an isolation transformer 
A) a step-down transformer 
B) a step-up transformer 
C) a power transformer 
D) an isolation transformer

Question 5

An autotransformer differs from most transformers in that:

Accepted Answer

A) it does not isolate the primary voltage from the secondary voltage. 
B) primary and secondary windings are the same. 
C) source current flows through both the windings. 
D) all of these. 
A) it does not isolate the primary voltage from the secondary voltage. 
B) primary and secondary windings are the same. 
C) source current flows through both the windings. 
D) all of these.

Question 6

-In Figure 14-1, if the secondary current is 50 mA, the reflected resistance seen by the primary equals ________.

Accepted Answer

A)    
B)    
C)    
D)    
A)    
B)    
C)    
D)

Question 7

-In Figure 14-1, if there are five times more turns in the primary than in the secondary, then what is the secondary voltage?

Accepted Answer

A) 120 V 
B) 12 V 
C) 24 V 
D) 600 V 
A) 120 V 
B) 12 V 
C) 24 V 
D) 600 V

Question 8

The efficiency of all transformers is very low.

Accepted Answer

A) True 
 B)False

Question 9

The impedance matching characteristic for a transformer is needed for a situation where maximum
power transfer to the load is desired.

Accepted Answer

A) True 
 B)False

Question 10

Eddy current loss in a transformer is ________.

Accepted Answer

A) due to current flowing in the core 
B) caused by rapid reversal of the magnetic field 
C) another name for flux leakage loss 
D) caused by the resistance of the wire 
A) due to current flowing in the core 
B) caused by rapid reversal of the magnetic field 
C) another name for flux leakage loss 
D) caused by the resistance of the wire

Question 11

The small dot placed on schematics of transformers indicates:

Accepted Answer

A) the phase of the voltages. 
B) the polarity of the voltages. 
C) the direction of the winding. 
D) all of these. 
A) the phase of the voltages. 
B) the polarity of the voltages. 
C) the direction of the winding. 
D) all of these.

Question 12

Which winding will have the lowest measured resistance in a transformer with four secondary windings?

Accepted Answer

A) the 5 V secondary 
B) the 12 V secondary 
C) the 6.3 V secondary 
D) the 550 V secondary 
A) the 5 V secondary 
B) the 12 V secondary 
C) the 6.3 V secondary 
D) the 550 V secondary

Question 13

A center tap transformer has a connection at the midpoint of the secondary winding resulting in:

Accepted Answer

A) two 180 degree out of phase secondary voltages. 
B) secondary voltages half that of a non-center tapped transformer with the same turns ratio. 
C) two equal magnitude secondary voltages. 
D) all of these. 
A) two 180 degree out of phase secondary voltages. 
B) secondary voltages half that of a non-center tapped transformer with the same turns ratio. 
C) two equal magnitude secondary voltages. 
D) all of these.

Question 14

When the turns ratio of a transformer is 1:10 and the primary AC voltage in 6 V, then the secondary voltage is ________.

Accepted Answer

A) 6 V 
B) 36 V 
C) 60 V 
D) 0.6 V 
A) 6 V 
B) 36 V 
C) 60 V 
D) 0.6 V

Question 15

The hysteresis loss in a transformer is ________.

Accepted Answer

A) caused by the resistance of the wire 
B) caused by rapid reversal of the magnetic field 
C) another name for flux leakage loss 
D) caused by current flowing in the core 
A) caused by the resistance of the wire 
B) caused by rapid reversal of the magnetic field 
C) another name for flux leakage loss 
D) caused by current flowing in the core

Question 16

36 V of dc is applied to a windings ratio of 1:2. What is the secondary voltage?

Accepted Answer

A) something slightly less than 72 V since transformers do have some loss 
B) 144 V 
C) 72 V 
D) none of the above 
A) something slightly less than 72 V since transformers do have some loss 
B) 144 V 
C) 72 V 
D) none of the above

Question 17

Only the number of turns in the primary and secondary of a transformer determines the actual
secondary voltage.

Accepted Answer

A) True 
 B)False

Question 18

The reflected load in a transformer is defined as the actual load as it appears to the source and results from:

Accepted Answer

A) the voltage ratio. 
B) the power ratio. 
C) the current ratio. 
D) the turns ratio. 
A) the voltage ratio. 
B) the power ratio. 
C) the current ratio. 
D) the turns ratio.

Question 19

The primary to secondary resistance should be relatively low.

Accepted Answer

A) True 
 B)False

Question 20

The relationship for the impedance matching ratio   in a transformer is:

Accepted Answer

A)    
B)    squared. 
C)    quared. 
D)    
A)    
B)    squared. 
C)    quared. 
D)

Exam 14: Transformers

An ideal 10:1 transformer with 20 VA of power has less than 2 VA on the output.

-In Figure 14-1, if the primary to secondary turns ratio is 7.5:1, the output voltage equals ________.

-When a 1 load resistor is connected across the secondary winding of a transformer with a turns ratio of 1:2, the source ʺseesʺ a reflected load of ________.

To couple two circuits together with no change in either voltage or current, use ________.

An autotransformer differs from most transformers in that:

-In Figure 14-1, if the secondary current is 50 mA, the reflected resistance seen by the primary equals ________.

-In Figure 14-1, if there are five times more turns in the primary than in the secondary, then what is the secondary voltage?

The efficiency of all transformers is very low.

The impedance matching characteristic for a transformer is needed for a situation where maximum power transfer to the load is desired.

Eddy current loss in a transformer is ________.

The small dot placed on schematics of transformers indicates:

Which winding will have the lowest measured resistance in a transformer with four secondary windings?

A center tap transformer has a connection at the midpoint of the secondary winding resulting in:

When the turns ratio of a transformer is 1:10 and the primary AC voltage in 6 V, then the secondary voltage is ________.

The hysteresis loss in a transformer is ________.

36 V of dc is applied to a windings ratio of 1:2. What is the secondary voltage?

Only the number of turns in the primary and secondary of a transformer determines the actual secondary voltage.

The reflected load in a transformer is defined as the actual load as it appears to the source and results from:

The primary to secondary resistance should be relatively low.

The relationship for the impedance matching ratio in a transformer is:

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