Question 1

To match a   audio load to a   speaker system, the primary of the impedance matching transformer must have ________ more turns than the secondary.

Accepted Answer

A) 150 
B) 12.2 
C) 3.06 
D) The primary should have less turns than the secondary. 
A) 150 
B) 12.2 
C) 3.06 
D) The primary should have less turns than the secondary.

Question 2

Autotransformers cannot be used for isolation purposes since there is only one winding.

Accepted Answer

A) True 
 B)False

Question 3

The turns ratio required to match a   source to a   load is ________.

Accepted Answer

A) 4:1 
B) 1:2 
C) 1:4 
D) 2:1 
A) 4:1 
B) 1:2 
C) 1:4 
D) 2:1

Question 4

-What is the secondary current in Figure 14-1 with a   load resistor and 4:1 turns ratio?

Accepted Answer

A) 600 mA 
B) 1.66 A 
C) 9.6 A 
D) 4.8 A 
A) 600 mA 
B) 1.66 A 
C) 9.6 A 
D) 4.8 A

Question 5

A transformer with a turns ratio of 1:1 is often used to isolate a load from a source.

Accepted Answer

A) True 
 B)False

Question 6

An air core transformer would most likely be used for:

Accepted Answer

A) isolation. 
B) audio frequencies 
C) impedance matching 
D) radio frequencies. 
A) isolation. 
B) audio frequencies 
C) impedance matching 
D) radio frequencies.

Question 7

-In Figure 14-1, if the primary to secondary turns ratio is changed to 4:1 and a 1   load resistor is in the secondary, the secondary current equals ________.

Accepted Answer

A) 30 mA 
B) 240 mA 
C) 120 mA 
D) 480 mA 
A) 30 mA 
B) 240 mA 
C) 120 mA 
D) 480 mA

Question 8

-What is the reflected resistance seen by the primary in Figure 14-1 if the turns ratio is 3:1 and   is 240 mA?

Accepted Answer

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

Question 9

Although the input voltage to the transformerʹs primary is correct, the transformer is outputting zero volts. A probable trouble is ________.

Accepted Answer

A) an open primary 
B) a partially shorted primary 
C) a shorted primary 
D) a partially shorted secondary 
A) an open primary 
B) a partially shorted primary 
C) a shorted primary 
D) a partially shorted secondary

Question 10

-In Figure 14-1, the primary to secondary turns ratio is 1:3 and the secondary current equals 120 mA. What is the primary current?

Accepted Answer

A) 180 mA 
B) 40 mA 
C) 360 mA 
D) cannot compute because the voltage is not given 
A) 180 mA 
B) 40 mA 
C) 360 mA 
D) cannot compute because the voltage is not given

Question 11

Transformers ________.

Accepted Answer

A) match the impedance of a source to the impedance of a load 
B) convert a higher voltage into a lower voltage 
C) convert a lower current into a higher current 
D) all of these 
A) match the impedance of a source to the impedance of a load 
B) convert a higher voltage into a lower voltage 
C) convert a lower current into a higher current 
D) all of these

Question 12

A step-down transformer could have a primary-secondary turns ratio of 4:1.

Accepted Answer

A) True 
 B)False

Question 13

A transformer with a turns ratio of 1:7 is a step down transformer.

Accepted Answer

A) True 
 B)False

Question 14

-What is the secondary voltage in Figure 14-1 if the turns ratio is 7:1?

Accepted Answer

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

Question 15

-What is the secondary voltage in Figure 14-1 if the turns ratio is 4.5:1?

Accepted Answer

A) 26.7 V 
B) 4.72 V 
C) 540 V 
D) 5.92 V 
A) 26.7 V 
B) 4.72 V 
C) 540 V 
D) 5.92 V

Question 16

The relationship for the voltage ratio   in a transformer is:

Accepted Answer

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

Question 17

A core material is not always necessary for proper operation of a transformer.

Accepted Answer

A) True 
 B)False

Question 18

-In Figure 14-1, if a load resistor of   is placed in the secondary circuit, what is the secondary current?

Accepted Answer

A) 533 mA 
B) 16 A 
C) 4.8 A 
D) 5.33 A 
A) 533 mA 
B) 16 A 
C) 4.8 A 
D) 5.33 A

Question 19

How can the windings ratio be safely determined for an unmarked transformer?

Accepted Answer

A) Standardized wire color codes indicate windings ratio. 
B) The turns ratio is the same as the ratio of primary resistance to secondary resistance ratio. 
C) Apply known low voltage ac to the primary and measure the secondary output. The ratio of the voltages is the same as the windings ratio. 
D) either A or C 
A) Standardized wire color codes indicate windings ratio. 
B) The turns ratio is the same as the ratio of primary resistance to secondary resistance ratio. 
C) Apply known low voltage ac to the primary and measure the secondary output. The ratio of the voltages is the same as the windings ratio. 
D) either A or C

Question 20

-What is the secondary voltage in Figure 14-1 if the turns ratio is 1:3?

Accepted Answer

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

Exam 14: Transformers

To match a audio load to a speaker system, the primary of the impedance matching transformer must have ________ more turns than the secondary.

Autotransformers cannot be used for isolation purposes since there is only one winding.

The turns ratio required to match a source to a load is ________.

-What is the secondary current in Figure 14-1 with a load resistor and 4:1 turns ratio?

A transformer with a turns ratio of 1:1 is often used to isolate a load from a source.

An air core transformer would most likely be used for:

-In Figure 14-1, if the primary to secondary turns ratio is changed to 4:1 and a 1 load resistor is in the secondary, the secondary current equals ________.

-What is the reflected resistance seen by the primary in Figure 14-1 if the turns ratio is 3:1 and is 240 mA?

Although the input voltage to the transformerʹs primary is correct, the transformer is outputting zero volts. A probable trouble is ________.

-In Figure 14-1, the primary to secondary turns ratio is 1:3 and the secondary current equals 120 mA. What is the primary current?

Transformers ________.

A step-down transformer could have a primary-secondary turns ratio of 4:1.

A transformer with a turns ratio of 1:7 is a step down transformer.

-What is the secondary voltage in Figure 14-1 if the turns ratio is 7:1?

-What is the secondary voltage in Figure 14-1 if the turns ratio is 4.5:1?

The relationship for the voltage ratio in a transformer is:

A core material is not always necessary for proper operation of a transformer.

-In Figure 14-1, if a load resistor of is placed in the secondary circuit, what is the secondary current?

How can the windings ratio be safely determined for an unmarked transformer?

-What is the secondary voltage in Figure 14-1 if the turns ratio is 1:3?

Quantities and Units

Voltage, Current, and Resistance

Ohms Law

Energy and Power

Series Circuits

Parallel Circuits

Series-Parallel Circuits

Circuit Theorems and Conversions

Branch, Loop, and Node Analyses

Magnetism and Electromagnetism

Introduction to Alternating Current and Voltage

Capacitors

Inductors

RC Circuits

RL Circuits

RlC Circuits and Resonance

Passive Filters

Circuit Theorems in Ac Analysis

Time Response of Reactive Circuits

Three-Phase Systems in Power Applications

Filters