369587509-Quiz-Question-and-answers-for-Electrical-docx

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For quantities and units

1. When these numbers are multiplied, (6 × 10 3 ) (5 × 10 5 ), the result is

A.

3 × 10 8

B.

30 × 10 8

C.

300 × 10 9

D.

3,000 × 10 7

Answer: Option B

2. Resistance is measured in

A.

henries

B.

ohms

C.

hertz

D.

watts


3. The number 65,000 expressed in scientific notation as a number between 1 and 10 times a power of ten is

A.

0.65 × 10 4

B.

6.5 × 10 4

C.

65 × 10 4

D.

650 × 10 3


4. When converting 7,000 nA to microamperes, the result is

A.

0.007 µA

B.

0.7 µA

C.

700 µA

D.

7 µA

Answer: Option

5. The number of kilowatts in 135 milliwatts is

A.

1.35 × 10 –4 kW

B.

135 × 10 –3 kW

C.

0.0135 kW

D.

0.00135 kW

Answer: Option A

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.

6. The number 4.4 × 10 6 ohms expressed using a metric prefix is

A.

4 k

B.

4.4 k

C.

4 M

D.

4.4 M

Answer: Option D

7. The number of microamperes in 2 milliamperes is

A.

2 µA

B.

20 µA

C.

200 µA

D.

2,000 µA


8. The number of millivolts in 0.06 kilovolts is

A.

600 V

B.

6,000 mV

C.

60,000 mV

D.

600,000 mV

Answer: Option C

9. Eighteen thousand watts is the same as

A.

18 mW

B.

18 MW

C.

18 kW

D.

18 µW


10. The number 3.2 × 10 –5 A expressed using a metric prefix is

A.

32 µA

B.

3.3 µA

C.

320 mA

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D.

3,200 mA


11. When converting 0.16 mA to microamperes, the result is

A.

16 µA

B.

160 µA

C.

1,600 µA

D.

0.0016 µA


12. When these numbers are added, (87 × 10 5 ) + (2.5 × 10 6 ), the result is

A.

1.12 × 10 4

B.

11.2 × 10 5

C.

112 × 10 5

D.

1,120 × 10 6


13. The quantity 3.3 × 10 3 is the same as

A.

330

B.

3,300

C.

33,000

D.

0.0033


14. Which of the following is not an electrical quantity?

A.

voltage

B.

current

C.

distance

D.

power


15. Seven thousand volts can be expressed as

A.

7 kV

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B.

7 MV

C.

7 mV

D.

either 7 kV or 7 mV


16. The number 4,500,000 can be expressed as

A.

4,500 × 10 6

B.

4.5 × 10 6

C.

4.5 × 10 -3

D.

either 4,500 × 10 4 or 4.5 × 10 6


17. When converting 1,600 kilohms to megohms, the result is

A.

1,600,000 M

B.

160 M

C.

1.6 M

D.

0.160 M


18. What is (79 × 10 6 )/(12 × 10 –8 )?

A.

6,580 × 10 12

B.

658 × 10 10

C.

6.58 × 10 14

D.

0.658 × 10 16


19. Fourteen milliamperes can be expressed as

A.

14 MA

B.

14 µA

C.

14 kA

D.

14 mA


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20. The number 4.38 × 10 –3 expressed as a number having a power of 10 –6 is

A.

4,380 × 10 –6

B.

438 × 10 –6

C.

43,800 × 10 –6

D.

438,000 × 10 –6


.

21. Voltage is measured in

A.

volts

B.

farads

C.

watts

D.

ohms


22. The number 0.0003 multiplied by 10 -3 is

A.

0.0000003

B.

0.0003

C.

3

D.

3,000


23. The number of megohms in 0.03 kilohms is

A.

0.00002 M

B.

0.0002 M

C.

3 × 10 –5 M

D.

either 0.00002 M or 0.0002 M


24. The quantity 43 × 10 -3 is the same as

A.

0.043

B.

0.430

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C.

430

D.

43,000


25. Current is measured in

A.

watts

B.

volts

C.

henries

D.

amperes

Answer: Option D .

Ohm's Law

1. An electric heater draws 3.5 A from a 110 V source. The resistance of the heating element is approximately

A.

385

B.

38.5

C.

3.1

D.

31


2. If 750 µA is flowing through 11 k of resistance, what is the voltage drop across the resistor?

A.

8.25 V

B.

82.5 V

C.

14.6 V

D.

146 V


3. The formula to find I when the values of V and R are known is

A.

I = VR

B.

I = R/V

C.

V = IR

D.

I = V/R


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4. A resistor is connected across a 50 V source. What is the current in the resistor if the color code is red, orange, orange, silver?

A.

2 mA

B.

2.2 mA

C.

214 mA

D.

21.4 mA


5. Approximately how many milliamperes of current flow through a circuit with a 40 V source and 6.8 k of resistance?

A.

27.2 mA

B.

59 mA

C.

5.9 mA

D.

590 mA


6. How much resistance is required to limit the current from a 12 V battery to 3.6 mA?

A.

3.3 k

B.

33 k

C.

2.2 k

D.

22 k


7. What is the voltage source for a circuit carrying 2 A of current through a 36 resistor?

A.

1.8 V

B.

18 V

C.

7.2 V

D.

72 V


8. What is the approximate resistance setting of a rheostat in which 650 mA of current flows with a 150 V source?

A.

9.7

B.

97

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C.

23

D.

230


9. How much voltage is needed to produce 2.5 A of current through a 200

resistor?

A.

50 V

B.

500 V

C.

80 V

D.

8 V


10. When there is 12 mA of current through a 1.2 k resistor, the voltage across the resistor is

A.

14.4 V

B.

1.4 V

C.

100 V

D.

10 V


Explanation:

V = IR (Ohms Law)

= 12 X 10 -3 X 1.2 X 10 3

= 12 X 1.2

= 14.4 V

11. A resistance of 3.3 M is connected across a 500 V source. The resulting current is approximately

A.

15.1 µA

B.

151 µA

C.

66 mA

D.

660 mA


12. You are measuring the current in a circuit that is operated on an 18 V battery. The ammeter reads 40 mA.

Later you notice the current has dropped to 20 mA. How much has the voltage changed?

A.

9 V

B.

900 mV

C.

0 V

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D.

18 V


13. The current through a flashlight bulb is 40 mA and the total battery voltage is 4.5 V. The resistance of the bulb is approximately

A.

112

B.

11.2

C.

1.2

D.

18


14. If you wish to increase the amount of current in a resistor from 120 mA to 160 mA by changing the 24 V source, what should the new voltage setting be?

A.

8 V

B.

320 V

C.

3.2 V

D.

32 V


15. If 24 V are applied across a resistor and there are 10.9 mA of current, the resistance is

A.

220 k

B.

22 k

C.

2.2 k

D.

220


16. How much resistance is needed to draw 17.6 mA from a 12 volt source?

A.

212

B.

6.8 k

C.

68

D.

680

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17. How much current is produced by a voltage of 18 kV across a 15 k

resistance?

A.

1.2 A

B.

12 A

C.

120 mA

D.

12 mA


18. A current of 200 µA through a 6.8 k resistor produces a voltage drop of

A.

34.4 V

B.

340 V

C.

13.6 V

D.

1.36 V


19. Four amperes of current are measured through a 24 resistor connected across a voltage source. How much voltage does the source produce?

A.

960 V

B.

9.6 V

C.

96 V

D.

8 V


20. Twelve volts are applied across a resistor. A current of 3 mA is measured. What is the value of the resistor?

A.

4

B.

400

C.

4 k

D.

4.4


21. When 12 V are applied across a 68 resistor, the current is

A.

816 mA

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B.

17.6 mA

C.

176 mA

D.

8.16 mA


22. Approximately how much current flows through a 3.3 M resistor across a 30 V source?

A.

9 A

B.

90 A

C.

900

A

D.

9000 A


23. A 120 V lamp-dimming circuit is controlled by a rheostat and protected from excessive current by a 3 A fuse.

To what minimum resistance value can the rheostat be set without blowing the fuse? Assume a lamp resistance of 20 ohms.

A.

40

B.

4

C.

2

D.

20


24. What is the approximate filament resistance of a light bulb if it operates from a 110 V source and 0.6 A of current is flowing?

A.

183

B.

18.3

C.

66

D.

6.6


25. What is the approximate resistance of a rheostat if the voltage source is 18 V and the current is 220 mA?

A.

8.2 k

B.

820

C.

8.2

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D.

82


Series Circuits

1. When a fourth resistor is connected in series with three resistors, the total resistance

A.

increases by one-fourth

B.

increases

C.

decreases

D.

remains the same


2. A string of five series resistors is connected across a 6 V battery. Zero voltage is measured across all resistors except R

3

. The voltage across R

3

is

A.

0 V

B.

1.2 V

C.

6 V

D.

0.6 V


3. A series circuit consists of three resistors with values of 120 , 270 , and 330 . The total resistance is

A.

less than 120

B.

the average of the values

C.

720

D.

120


4. A certain series circuit consists of a 1/8 W resistor, a 1/4 W resistor, and a 1/2 W resistor. The total resistance is 1200 . If each resistor is operating in the circuit at its maximum power dissipation, total current flow is

A.

27 mA

B.

2.7 mA

C.

19 mA

D.

190 mA


Explanation:

Total P = P1 + P2 + P3 = 7/8w.

P = I 2 R.

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I = sqrt (P/R)

Now, P = 7/8w, R = 1200 ohm.

Therefore,

I= sqrt ( (7/8)/1200 ) = 0.0270030862 = 27 mA.

5. Which of the following series combinations dissipates the most power when connected across a 120 V source?

A.

one 220 resistor

B.

two 220 resistors

C.

three 220 resistors

D.

four 220 resistors


6. When one of three series resistors is removed from a circuit and the circuit is reconnected, the current

A.

increases

B.

increases by one-third

C.

decreases by one-third

D.

decreases by the amount of current through the removed resistor


7. The total power in a certain circuit is 12 W. Each of the four equal-value series resistors making up the circuit dissipates

A.

12 W

B.

48 W

C.

3 W

D.

8 W


8. The following resistors (one each) are connected in a series circuit: 470

, 680 , 1 k , and 1.2 k .

The voltage source is 20 V. Current through the 680 resistor is approximately

A.

60 mA

B.

30 mA

C.

6 mA

D.

300 mA


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9. A series circuit consists of a 4.7 k , a 12 k , and a 2.2 k resistor. The resistor that has the most voltage drop is

A.

the 12 k

B.

the 2.2 k

C.

the 4.7 k

D.

impossible to determine from the given information


10. All the voltage drops and the source voltage added together in a series circuit is equal to

A.

the total of the voltage drops

B.

the source voltage

C.

zero

D.

the total of the source voltage and the voltage drops


11. Two resistors are in series: a 5.6 k resistor and a 4.7 k resistor. The voltage drop across the 5.6 k resistor is 10 V. The voltage across the 4.7 k resistor is

A.

8.39 V

B.

10 V

C.

2.32 V

D.

0 V


12. Three 680

resistors are connected in series with a 470 V source. Current in the circuit is

A.

69 mA

B.

230 mA

C.

23 mA

D.

690 mA


13. There are five resistors in a given series circuit and each resistor has 6 V dropped across it. The source voltage

A.

is 6 V

B.

depends on the current flow

C.

depends on the resistor values

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D.

is 30 V


14. If a 6 V and a 9 V source are connected series aiding, the total voltage is

A.

6 V

B.

9 V

C.

3 V

D.

15 V


15. Five resistors are connected in a series and there is a current of 3 A into the first resistor. The amount of current into the second resistor is

A.

3 A

B.

1 A

C.

4 A

D.

0.3 A


.

16. The total resistance of eight 5.6 k

resistors in series is

A.

8

B.

5,600

C.

4,480

D.

44,800


17. A series circuit has a 24 V source and a total resistance of 120 . The current through each resistor is

A.

24 mA

B.

200 mA

C.

120 mA

D.

20 mA


18. To measure the current out of the second resistor in a circuit consisting of four resistors, an ammeter can be placed

A.

between the second and third resistors

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B.

at the negative terminal of the source

C.

between the third and fourth resistors

D.

at any point in the circuit


19. A 12 V battery is connected across a series combination of 68

, 47 , 220 , and 33 . The amount of current is

A.

326 mA

B.

16.3 mA

C.

32.6 mA

D.

163 mA


20. If a 24 V and a 6 V battery are series opposing, the total voltage is

A.

30 V

B.

24 V

C.

18 V

D.

0 V


21. A series circuit consists of three resistors. Two resistors are 1.2 k each. The total resistance is 12 k .

The value of the third resistor

A.

is 9,600

B.

is 960

C.

is 1.2 k

D.

cannot be determined


22. Four equal-value resistors are in series with a 12 V battery and 13.63 mA are measured. The value of each resistor is

A.

22

B.

220

C.

880

D.

88

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Explanation:

Total Resistance, r = 12 / 13.63

= 0.880 in ohms

Total Resistance, r= 880

Each resistance value = r/4

= 880/4

Each resistance value = 220 ohms

.

23. Two 1.5 V cells are connected series opposing across two 100

resistors in series. Total current flow is

A.

15 mA

B.

5 mA

C.

2 mA

D.

0 A


24. The total resistance of a circuit is 680 . The percentage of the total voltage appearing across a 47 resistor that makes up part of the total series resistance is

A.

68%

B.

47%

C.

69%

D.

6.91%


25. Two 6 V batteries are connected series aiding across two 1.2 k resistors in series. Current through each resistor is

A.

5 mA

B.

10 mA

C.

0 A

D.

2.5 mA


Series-Parallel Circuits

1. The internal resistance of a 20,000 ohm/volt voltmeter set on its 5 V range is

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A.

20,000

B.

100,000

C.

200,000

D.

1,000,000


2. Two 1.2 k

resistors are in series and this series combination is in parallel with a 3.3 k resistor. The total resistance is

A.

138

B.

1,389

C.

5,700

D.

880


3. The output of a certain voltage divider is 12 V with no load. When a load is connected, the output voltage

A.

decreases

B.

increases

C.

remains the same

D.

becomes zero


4. A certain voltage divider consists of two 12 k

resistors in series. Which of the following load resistors will have the most effect on the output voltage?

A.

1 M

B.

24 k

C.

18 k

D.

12 k


5. A voltage divider consists of two 68 k

resistors and a 24 V source. The unknown output voltage is

A.

12 V

B.

24 V

C.

0 V

D.

6 V

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6. Three 10 k resistors are connected in series. A 20 k resistor is connected in parallel across one of the

10 k resistors. The voltage source is 24 V. The total current in the circuit is

A.

900 A

B.

9 mA

C.

90 mA

D.

800

A


7. A certain voltage divider consists of three 1 k

resistors in series. Which of the following load resistors will have the least effect on the output voltage?

A.

1 M

B.

100 k

C.

1 k

D.

330


8. The parallel combination of a 470

resistor and a 1.5 k resistor is in series with the parallel combination of five 1 k resistors. The source voltage is 50 V. The percentage of the load current through any single 1 k resistor is

A.

25%

B.

20%

C.

100%

D.

50%


9. A certain Wheatstone bridge has the following resistor values:

R

1

The unknown resistance is

= 10 k , R

2

= 720 , and R

4

= 2.4 k .

A.

24

B.

2.4

C.

300

D.

3,000


10. On which of the following voltage range settings will a voltmeter present the minimum load on a circuit?

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A.

1 V

B.

50 V

C.

500 V

D.

1,000 V


11. The internal resistance of a 30,000 ohm/volt voltmeter set on its 50 V range is

A.

15,000

B.

150,000

C.

1,500,000

D.

15,000,000


12. The parallel combination of a 6.8 k resistor and a 10 k resistor is in series with the parallel combination of a 2.2 k resistor and a 1 k resistor. A 100 V source is connected across the circuit. The resistor(s) with the greatest voltage drop is (are)

A.

6.8 k

B.

2.2 k

C.

6.8 k and 10 k

D.

2.2 k and 1 k


13. When a load resistance is removed from the output of a voltage divider circuit, the current drawn from the source

A.

decreases

B.

increases

C.

remains the same

D.

is cut off


14. A certain circuit is composed of two parallel resistors. The total resistance is 1,403

. One of the resistors is 2 k . The other resistor value is

A.

1,403

B.

4.7 k

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C.

2 k

D.

3,403



resistor and a 680 resistor is in series with the parallel combination of four 2 k resistors. The total resistance is

A.

1,650

B.

1,078

C.

77.8

D.

778


16. A 12 k resistor, a 15 k resistor, and a 22 k resistor are in series with two 10 k resistors that are in parallel. The source voltage is 75 V. Current through the 15 k resistor is approximately

A.

14 mA

B.

1.4 mA

C.

5 mA

D.

50 mA


17. A 6 V battery output is divided down to obtain two output voltages. Three 2.2 k resistors are used to provide the two taps. The two output voltages are

A.

2 V, 4 V

B.

2 V, 2 V

C.

2 V, 6 V

D.

4 V, 6 V


18. Two 3.3 k resistors are in series and this series combination is in parallel with a 4.7 k resistor. The voltage across one of the 3.3 k resistors is 12 V. The voltage across the 4.7 k resistor is

A.

24 V

B.

12 V

C.

0 V

D.

6 V

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19. A balanced Wheatstone bridge consists of an

R

V value of R

UNK

is

of 3,500 , an R

2

of 200 , and an R

3

of 680 . The

A.

680

B.

1,029

C.

200

D.

880


20. In a certain five-step

R /2 R ladder network, the smallest resistor value is 1 k . The largest value is

A.

indeterminable

B.

2 k

C.

10 k

D.

20 k


21. A voltage divider consists of two 100 k resistors and a 12 V source. What will the output voltage be if a load resistor of 1 M is connected to the output?

A.

0.57 V

B.

6 V

C.

12 V

D.

5.7 V



resistor and a 1.2 k resistor is in series with the parallel combination of three 3 k resistors. A 200 V source is connected across the circuit. The resistor with the most current has a value of

A.

470 or 1.2 k

B.

3 k

C.

470

D.

1.2 k


Branch, Loop and Node Analyses

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1.

Find the node voltage V

A

.

A.

6 V

B.

12 V

C.

4.25 V

D.

3 V


2. What is the current through R

2

?

A.

3.19 A

B.

319 mA

C.

1.73 A

D.

173 mA


3. Find branch current IR

2

.

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A.

5.4 mA

B.

–5.4 mA

C.

113.0 mA

D.

119.6 mA


4. Find the node voltage V

A

.

A.

518 mV

B.

5.18 V

C.

9.56 V

D.

956 mV


5. Find I

2

.

4 I

1

6 I

1

+ 4 I

2

+ 7 I

2

= 2

= 4

A.

1 A

B.

–1 A

C.

100 mA

D.

–100 mA


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6. What is the voltage drop across R

1

?

A.

850 mV

B.

7.82 V

C.

9.18 V

D.

918 mV



2

?

A.

3.5 V

B.

4.18 V

C.

1.5 V

D.

145 mV


8. In assigning the direction of branch currents,

A.

the directions are critical

B.

the directions are not critical

C.

they must point into a node

D.

they must point out of a node


9. Find I

4 I

1

1

+ 4 I

.

2

= 2

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6 I

1

+ 7 I

2

= 4

A.

0.5 A

B.

50 mA

C.

–0.5 A

D.

–50 mA


10. Using the mesh current method, find the branch current, IR

1

, in the above figure.

A.

115 mA

B.

12.5 mA

C.

12.5 A

D.

135 mA


11. What is the current through R

2

?

A.

177 mA

B.

250 mA

C.

500 mA

D.

125 mA

Answer: Option A .

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12. The first row of a certain determinant has the numbers 3 and 5. The second row has the numbers 7 and 2.

The value of this determinant is

A.

31

B.

–31

C.

39

D.

–29


13. The first row of a certain determinant has the numbers 10 and 6. The second row has the numbers 3 and 5.

The value of this determinant is

A.

18

B.

50

C.

32

D.

–32



3

?

A.

112 mV

B.

11.25 V

C.

180 mV


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15. The expansion method for evaluating determinants is

A.

better than any other method

B.

good for only one determinant

C.

more flexible than the cofactor method

D.

good for second- and third-order determinants


16. The branch current method uses

A.

Kirchhoff's voltage and current laws

B.

Thevenin's theorem and Ohm's law

C.

Kirchhoff's current law and Ohm's law

D.

the superposition theorem and Thevenin's theorem


Alternating Current and Voltage

1. If the rms voltage drop across a 15 k

resistor is 16 V, the peak current through the resistor is

A.

15 mA

B.

1.5 mA

C.

10 mA

D.

1 mA


2. The conductive loop on the rotor of a simple two-pole, single-phase generator rotates at a rate of 400 rps.

The frequency of the induced output voltage is

A.

40 Hz

B.

100 Hz

C.

400 Hz

D.

indeterminable


3. How many degrees are there in /3 rad?

A.

6°

B.

60°

C.

180°

D.

27°

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4. To produce an 800 Hz sine wave, a four-pole generator must be operated at

A.

200 rps

B.

400 rps

C.

800 rps

D.

1,600 rps


5. One sine wave has a positive-going zero crossing at 15° and another sine wave has a positive-going zero crossing at 55°. The phase angle between the two waveforms is

A.

0°

B.

45°

C.

40°

D.

none of the above


6. If the rms current through a 4.7 k

resistor is 4 mA, the peak voltage drop across the resistor is

A.

4 V

B.

18.8 V

C.

26.6 V

D.

2.66 V


7. A pulse waveform has a high time of 8 ms and a pulse width of 32 ms. The duty cycle is

A.

25%

B.

50%

C.

1%

D.

100%


8. A 20 kHz pulse waveform consists of pulses that are 15 s wide. The duty cycle

A.

is 1%

B.

is 30%

C.

is 100%

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D.



9. If the peak of a sine wave is 13 V, the peak-to-peak value is

A.

6.5 V

B.

13 V

C.

26 V

D.

none of the above


10. A sinusoidal current has an rms value of 14 mA. The peak-to-peak value is

A.

45.12 mA

B.

16 mA

C.

39.6 mA

D.

22.6 mA


11. A signal with a 400 s period has a frequency of

A.

250 Hz

B.

2,500 Hz

C.

25,000 Hz

D.

400 Hz


12. A sine wave of 15 kHz is changing at a faster rate than a sine wave with a frequency of

A.

25 kHz

B.

12 kHz

C.

18 kHz

D.

1.3 MHz


13. The average value of a 12 V peak sine wave over one complete cycle is

A.

0 V

B.

1.27 V

C.

7.64 V

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D.

6.37 V


14. When a sine wave has a frequency of 100 Hz in 12 s it goes through

A.

1/100 cycle

B.

12 cycles

C.

120 cycles

D.

1,200 cycles


15. A sawtooth wave has a period of 10 ms. Its frequency is

A.

10 Hz

B.

50 Hz

C.

100 Hz

D.

1,000 Hz


16. Two series resistors are connected to an ac source. If there are 7.5 V rms across one resistor and 4.2 V rms across the other, the peak source voltage is

A.

16.54 V

B.

1.65 V

C.

10.60 V

D.

5.93 V


17. If a sine wave goes through 10 cycles in 20 s, the period is

A.

20 s

B.

4 s

C.

2 s

D.

100 s


18. A square wave has a period of 60 s. The first odd harmonic is

A.

5 kHz

B.

50 kHz

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C.

500 kHz

D.

33.33 kHz


19. Sine wave A has a positive-going zero crossing at 45°. Sine wave B has a positive-going zero crossing at

60°. Which of the following statements is true?

A.

Wave A leads wave B by 15°.

B.

Wave A lags wave B by 15°.

C.

Wave A leads wave B by 105°.

D.

Wave A lags wave B by 105°.


20. A phasor represents

A.

the magnitude and a quantity direction

B.

the width of a quantity

C.

the phase angle

D.

the magnitude of a quantity


21. A sine wave with a period of 4 ms is changing at a faster rate than a sine wave with a period of

A.

0.0045 s

B.

2 ms

C.

1.5 ms

D.

3,000 s


22. A waveform has a baseline of 3 V, a duty cycle of 20%, and an amplitude of 8 V. The average voltage value is

A.

4 V

B.

4.6 V

C.

1.6 V

D.

11 V


23. A sine wave with an rms value of 12 V is riding on a dc level of 18 V. The maximum value of the resulting waveform is

A.

6 V

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B.

30 V

C.

35 V

D.

0 V


24. If the rms current through a 6.8 k resistor is 8 mA, the rms voltage drop across the resistor is

A.

5.44 V

B.

54.4 V

C.

7.07 V

D.

8 V


25. The average half-cycle value of a sine wave with a 40 V peak is

A.

25.48 V

B.

6.37 V

C.

14.14 V

D.

50.96 V


Inductors

1. An inductance of 0.08

H is larger than

A.

0.0000008 H

B.

0.000000008 H

C.

0.000008 H

D.

0.00008 mH


2. A 240

H inductor is equivalent to a

A.

0.240 mH inductor

B.

0.000240 mH inductor

C.

240 mH inductor

D.

240 H inductor


3. A 2 mH, a 3.3 mH, and a 0.2 mH inductor are connected in series. The total inductance is

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A.

55 mH

B.

less than 0.2 mH

C.

less than 5.5 mH

D.

5.5 mH


4. A 5 mH, a 4.3 mH, and a 0.6 mH inductor are connected in parallel. The total inductance is

A.

9.9 mH

B.

greater than 5 mH

C.

9.9 mH or greater than 5 mH

D.

less than 0.6 mH


5. The voltage across a coil when di/dt = 20 mA/ s and L = 8 H is

A.

16 mV

B.

160 mV

C.

1.6 mV

D.

2.5 mV


6. A sine wave voltage is applied across an inductor. When the frequency of the voltage is decreased, the current

A.

is increased

B.

is decreased

C.

does not change

D.

momentarily goes to zero


7. Two 10 H inductors are in parallel and the parallel combination is in series with a third 10 H inductor. What is the approximate total reactance when a voltage with a frequency of 7 kHz is applied across the circuit terminals?

A.

219 k

B.

66 k

C.

660 k

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D.

1.3 M


8. An ohmmeter is connected across an inductor and the pointer indicates zero ohms. The inductor is

A.

good

B.

open

C.

shorted

D.

partly shorted


9. Two inductors,

L

1

and L

2

, are in parallel. L

1

has a value of 25 H and L

2

a value of 50 H. The parallel combination is in series with L

3

, a 20 H coil. The entire combination is across an ac source of 60 V

300 kHz. The total rms current is rms

at

A.

87 mA

B.

870 mA

C.

87 A

D.

337 mA


10. An inductor, a 1 k

resistor, and a switch are connected in series across a 6 V battery. At the instant the switch is closed, the inductor voltage is

A.

0 V

B.

6 V

C.

12 V

D.

4 V


11. The winding resistance of a coil can be increased by

A.

increasing the number of turns

B.

using a thinner wire

C.

changing the core material

D.

increasing the number of turns or using thinner wire


12. An inductance of 0.43 mH is smaller than

A.

43 H

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B.

430 H

C.

0.05 H

D.

0.00043 H


13. An inductor and a resistor are in series with a sine wave voltage source. The frequency is set so that the inductive reactance is equal to the resistance. If the frequency is increased, then

A.

V

R

≥ V

L

B.

V

L

< V

R

C.

V

L

= V

R

D.

V

L

> V

R


14. The current through a 120 mH coil is changing at a rate of 150 mA/s. The voltage induced across the coil is

A.

1.8 mV

B.

18 mV

C.

180 mV

D.

1.25 mV


15. When the current through an inductor decreases, the amount of energy stored in the electromagnetic field

A.

increases

B.

decreases

C.

remains the same

D.

doubles


16. Three 15 mH inductors are in series. The total inductance is

A.

15 mH

B.

30 mH

C.

45 mH

D.

5 mH


17. An 18 V power supply is connected across a coil with a winding resistance of 180

. Current flow in the coil is

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A.

1 mA

B.

10 mA

C.

100 mA

D.

1 A


18. A switch, a 220

resistor, and a 60 mH inductor are in series across a 20 V battery. What is the current through the inductor two time constants after the switch is closed?

A.

91 mA

B.

78 mA

C.

57 mA

D.

400 mA


19. A 320 value?

H coil is in series with a 3.3 k resistor. How long does it take for current to build up to its full

A.

0.48 s

B.

0.48 ms

C.

0.48 s

D.

48 s


20. Five inductors are connected in series. The lowest value is 8 μH. If the value of each inductor is twice that of the preceding one, and if the inductors are connected in order of ascending values, the total inductance is

A.

8 H

B.

32 μH

C.

64 μH

D.

248 μH


21. The inductance of an iron-core coil decreases if

A.

the number of turns is decreased

B.

the iron core is removed

C.

the length of the coil decreases

D.

none of the above


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22. The following coils are in parallel: 75

H, 40 H, 25 H, and 15 H. The total inductance is approximately

A.

6.9

H

B.

14 H

C.

2.2

H

D.

155 H


23. When the current through an inductor is cut in half, the amount of energy stored in the electromagnetic field

A.

is quartered

B.

quadruples

C.

doubles

D.

does not change


RC Circuits

1. In the complex plane, the number 14 – j 5 is located in the

A.

first quadrant

B.

second quadrant

C.

third quadrant

D.

fourth quadrant


2. Point +4 on the complex plane is

A.

4 units above the origin on the j axis

B.

4 units below the origin on the j axis

C.

4 units right of the origin on the real axis

D.

4 units left of the origin on the real axis


3. A 470 resistor and a 0.2 rectangular form, is

F capacitor are in parallel across a 2.5 kHz ac source. The admittance, Y , in

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A.

212

B.

2.12 mS + j 3.14 mS

C.

3.14 mS + j 2.12 mS

D.

318.3


4. A positive angle of 30° is equivalent to a negative angle of

A.

–30°

B.

–330°

C.

–60°

D.

–180°


5. In a series RC circuit, 12 V

(rms)

The rms source voltage is

is measured across the resistor and 15 V

(rms)

is measured across the capacitor.

A.

3 V

B.

27 V

C.

19.2 V

D.

1.9 V


6. A 6 kHz sinusoidal voltage is applied to a series RC circuit. The frequency of the voltage across the resistor is

A.

0 Hz

B.

12 kHz

C.

6 kHz

D.

18 kHz


7. The voltages in Problem 4 are measured at a certain frequency. To make the capacitor voltage greater than the resistor voltage, the frequency

A.

must be increased

B.

must be decreased

C.

is held constant

D.

has no effect


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8. In the complex plane, the number 4 + j 3 is located in the

A.

first quadrant

B.

second quadrant

C.

third quadrant

D.

fourth quadrant


9. When the frequency of the source voltage decreases, the impedance of a parallel RC circuit

A.

increases

B.

decreases

C.

does not change

D.

decreases to zero


10. A 47

resistor and a capacitor with a capacitive reactance of 120 are in series across an ac source.

What is the circuit impedance, Z ?

A.

129

B.

12.9

C.

167

D.

73


11. What is the value of the hypotenuse of a right triangle whose sides are 12 and 18?

A.

4.24

B.

3.46

C.

2.16

D.

21.63


12. The complex number 6 + j 6 is equivalent to

A.

6 45°

B.

36 45°

C.

8.48

45°

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D.

8.48

90°


13. In a parallel RC circuit, there is 100 mA through the resistive branch and 100 mA through the capacitive branch. The total rms current is

A.

200 mA

B.

100 mA

C.

282 mA

D.

141 mA


14. An ac circuit consists of a resistor and a capacitor. To increase the phase angle above 45°, the following condition must exist:

A.

R = X

C

B.

R > X

C

C.

R < X

C

D.

R = 5 X

C


15. What is the angular difference between + j 4 and – j 4?

A.

30°

B.

90°

C.

180°

D.

270°


16. A resistor and a capacitor are in series across a 20 V ac source. Circuit impedance is 4.33 k . Current flow in the circuit is

A.

9.2 mA

B.

92 mA

C.

4.6 mA

D.

460 mA


17. For a certain load, the true power is 150 W and the reactive power is 125 VAR. The apparent power is

A.

19.52 W

B.

195.2 W

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C.

275 W

D.

25 W


18. When the frequency of the voltage applied to a series RC circuit is increased, the phase angle

A.

increases

B.

decreases

C.

remains the same

D.

becomes erratic


19. In a series RC circuit, when the frequency and the resistance are halved, the impedance

A.

doubles

B.

is halved

C.

is reduced to one-fourth

D.

cannot be determined without values


20. A 2 k resistor is in series with a 0.015 of the total impedance and the phase angle?

F capacitor across a 15 kHz ac source. What is the magnitude

A.

73.4 and θ = –19.5°

B.

707 and θ = –19.5°

C.

2121 and θ = –19.5°

D.

734 and θ = –38.9°


Explanation:

Xc = 1/2πfC = 707 Ω

Z = R - jXc = 2000 - j(707)

|z| = sqrt(R*R + Xc*Xc) = 2121 Ω

Phase angle = arctangent(Xc/R) = 19.5°

21. A 12 k resistor is in series with a 0.02

F capacitor across a 1.2 kHz ac source. If the current is expressed in polar form as I = 0.3

0° mA, what is the source voltage expressed in polar form?

A.

45.6 V

B.

411.3 V

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C.

0.411 V

D.

4.11 V


22. The complex number 40 55° is equivalent to

A.

55 + j 55

B.

40 + j 40

C.

45.88 + j 65.52

D.

22.94 + j 32.76


23. A 120 resistor is in parallel with a capacitor with a capacitive reactance of 40 . Both components are across a 12 V ac source. What is the magnitude of the total impedance?

A.

37.9

B.

3.7

C.

14,400

D.

4,800


24. A 47 resistor and a capacitor with 150 of capacitive reactance are in series across an ac source. The impedance, expressed in rectangular form, is

A.

Z = 47 + j 150

B.

Z = 47 – j 150

C.

Z = 197

D.

Z = 103


25. A 2 k resistor and a 0.002

F capacitor are in series across an ac source. Current in the circuit is 6.50 mA. The true power is

A.

84.5 mW

B.

845 mW

C.

13 mW

D.

130 mW


26. A capacitor with 150 of capacitive reactance is across an ac source. The impedance, expressed in polar

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https://sites.google.com/site/sdmservice15/ form, is

A.

Z = 150

B.

Z = 150 90°

C.

Z = 150 –90°

D.

Z = 150 180°


27. When the frequency of the voltage applied to a series RC circuit is decreased, the impedance

A.

increases

B.

decreases

C.

remains the same

D.

doubles


RLC Circuits and Resonance

1. A 10 resistor, a 90 mH coil, and a 0.015 impedance magnitude at 1,200 Hz below f r

is

F capacitor are in series across an ac source. The

A.

1,616

B.

161

C.

3,387

D.

1,771


2. In a series RLC circuit that is operating above the resonant frequency, the current

A.

lags the applied voltage

B.

leads the applied voltage

C.

is in phase with the applied voltage

D.

is zero


3. A 15 resistor, a 220

H coil, and a 60 pF capacitor are in series across an ac source. What is the bandwidth of the circuit?

A.

138 MHz

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B.

10,866 Hz

C.

1,907 Hz

D.

138 kHz


4. A resistor of 3 k , a 0.05

F capacitor, and a 120 mH coil are in series across a 5 kHz, 20 V ac source.

What is the impedance, expressed in polar form?

A.

636

B.

3,769

C.

433

D.

4,337


5. A 12 resistor, a 40 frequency is

F capacitor, and an 8 mH coil are in series across an ac source. The resonant

A.

28.1 Hz

B.

281 Hz

C.

2,810 Hz

D.

10 kHz


6. The impedance at the resonant frequency of a series

RLC circuit with L = 20 mH, C = 0.02 F, and R

W

=

90 is

A.

0

B.

90

C.

20 k

D.

40 k


7. A 6.8 k resistor, a 7 mH coil, and a 0.02

F capacitor are in parallel across a 17 kHz ac source. The coil's internal resistance, R

W

, is 30 . The equivalent parallel resistance, R p

(eq), is

A.

1,878

B.

18,780

C.

18,750

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D.

626


8. Referring to Problem 20, what is the total parallel resistance ( R p(tot)

)?

A.

4.99

B.

499

C.

4,992

D.

6,800


9. A 200 resistor, a coil with 30 of reactance, and a capacitor of unknown reactance are in series across an ac source. The circuit is at resonance. Circuit impedance

A.

is 230

B.

is 170

C.

is 200

D.



10. Referring to Problem 8, the total current is

A.

1.5 A

B.

573 mA

1. If the resistance in parallel with a parallel resonant circuit is reduced, the bandwidth

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C.

5.73 A

D.

1.19 A


A.

disappears

B.

becomes sharper

C.

increases

D.

decreases


12. A 90 resistor, a coil with 30 of reactance, and a capacitor with 50 of reactance are in series across a 12 V ac source. The current through the resistor is

A.

9 mA

B.

90 mA

C.

13 mA

D.

130 mA


13. A resonant circuit has a lower critical frequency of 7 kHz and an upper critical frequency of 13 kHz. The bandwidth of the circuit is

A.

7 kHz

B.

13 kHz

C.

20 kHz

D.

4 kHz


14. If the value of C in a series RLC circuit is decreased, the resonant frequency

A.

is not affected

B.

increases

C.

is reduced to zero

D.

decreases


15. A 24 resistor, an inductor with a reactance of 120 , and a capacitor with a reactance of 120 are in series across a 60 V source. The circuit is at resonance. The voltage across the inductor is

A.

60 V

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B.

660 V

C.

30 V

D.

300 V


16. To tune a parallel resonant circuit to a higher frequency, the capacitance should be

A.

increased

B.

decreased

C.

left alone

D.

replaced with inductance


17. In a certain series resonant circuit, V

C

= 125 V, V

L

= 125 V, and V

R

= 40 V. The value of the source voltage is

A.

125 V

B.

250 V

C.

290 V

D.

40 V


18. A certain series resonant circuit has a bandwidth of 2 kHz. If the existing coil is replaced with one having a higher value of Q , the bandwidth will

A.

increase

B.

remain the same

C.

decrease

D.

be less selective


19. A 9 mH coil is in parallel with a 0.015

F capacitor across an 18 kHz ac source. The coil's internal resistance, R

W

, is 60 . The circuit impedance is

A.

17,340

B.

1,734

C.

290

D.

1,018


20. A 15 resistor, an inductor with 8 inductive reactance, and a capacitor with 12 capacitive reactance are in parallel across an ac voltage source. The circuit impedance is

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A.

12.7

B.

127

C.

4,436

D.

6,174


A certain series RLC circuit with a 200 Hz, 15 V ac source has the following values: R = 12 , C = 80

F, and L = 10 mH. The total impedance, expressed in polar form, is

A.

12.28

12.34°

B.

12.57

12.34°

C.

9.95

12.34°

D.

12.62

12.34°

Answer: Option A

Circuit Theorems in AC Analysis

1. Determine

V

TH

when R

1

is 180 and X

L

is 90 .

A.

135 63.4° V

B.

13.5

63.4° V

C.

12.2

0° V

D.

122 0° V


2. For the given circuit, find V

TH

for the circuit external to R

L

.

A.

4.69

51.3° V

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B.

4.69

38.7° V

C.

469 38.7° mV

D.

6 0° V


3. Referring to the given circuit, find Z

TH

if R is 15 k and R

L

is 38 k .

A.

89.82 –51.3° k

B.

19.2 –38.3° k

C.

9.38

–51.3° k

D.

180 –38.3° k


4. For the circuit shown, determine Z

TH

for the portion of the circuit external to R

L

.

A.

66.7 –33.7° k

B.

6.67

–333.7° k

C.

14.4 –56.3° k

D.

1.44 –33.7° k


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5. Referring to the given circuit, what is Z

TH

if R

1

is changed to 220 ?

A.

225 12.1°

B.

225 77.9°

C.

46 77.9°

D.

46 12.1°


6. Determine V

TH

for the circuit external to R

L

in the given figure.

A.

135 63.4° V

B.

13.5

63.4° V

C.

13.5

0° V

D.

135 0° V


52 SDM SERVICES


A.

1488 –70.7°

B.

3859 –31.2°

C.

5180 –50.5°

D.

1828 –50.2°


8. The two basic components of a Thevenin equivalent ac circuit are

A.

the equivalent voltage source and the equivalent series impedance

B.

the equivalent voltage source and the equivalent series resistance

C.

the equivalent voltage source and the equivalent parallel impedance

D.

the equivalent voltage source and the equivalent parallel resistance



TH

if V

S

is 18 0° V.

A.

9.82 –51.3° k

B.

9.38

–51.3° k

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C.

180 –38.3° k

D.

19.2 –38.3° k


10. In applying the superposition theorem,

A.

the sources are considered one at a time with all others replaced by their internal impedance

B.

all sources are considered independently

C.

all sources are considered simultaneously

D.

the sources are considered one at a time with all others replaced by their internal resistance


11. If two currents are in the same direction at any instant of time in a given branch of a circuit, the net current at that instant

A.

is zero

B.

is the sum of the two currents

C.

is the difference between the two currents

D.



12. The Thevenin equivalent voltage is

A.

equal to the source voltage

B.

the same as the load voltage

C.

the open circuit voltage

D.

none of the above


13. Referring to the given circuit, L

A.

must be in parallel with R

L

B.

must be placed in parallel with V

S

C.

must have a reactance equal to X

C

D.

has no effect on the result


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TH

for the part of the circuit that is external to R

L

.

A.

129 21.4°

B.

43.7

68.6°

C.

43.7

21.4°

D.

12.9

68.6°


15. In order to get maximum power transfer from a capacitive source, the load must

A.

have a capacitive reactance equal to circuit resistance

B.

have an impedance that is the complex conjugate of the source impedance

C.

be as capacitive as it is inductive

D.

none of the above


16. Referring to the given circuit, determine Z

TH

as seen by R

L

.

A.

1444 –48.5°

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B.

4176 –73.3°

C.

956 –48.5°

D.

1444 –73.3°


17. Referring to the given circuit, how much power, in watts, is delivered to the speaker at the determined frequency if V

S

= 4.5 V

RMS

?

A.

226 mW

B.

2.26 mW

C.

4.24 mW

D.

424 mW


18. The Norton equivalent current is

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A.

the current through the load

B.

the open-current from the source

C.

the short circuit current

D.

none of the above


19. Determine

V

TH

if R

1

is changed to 3.3 k .

A.

0.574

16.7° V

B.

4.63

16.7° V

C.

4.63

39.5° V

D.

0.463

39.5° V


20. Referring to the given circuit, what is V

TH

if V

S

= 12 0° V?

A.

4.69

38.7° V

B.

9.38

38.7° V

C.

12 0° V

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D.

6 0° V


21. For the circuit given, determine the Thevenin voltage as seen by R

L

.

A.

0.574

16.7° V

B.

5.74

16.7° V

C.

0.574 –16.7° V

D.

5.74

–16.7° V


22. Determine the frequency at which the maximum power is transferred from the amplifier to the speaker in the given figure.

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A.

1,027 Hz

B.

10,270 Hz

C.

6,330 Hz

D.

63,330 Hz


23. Norton's theorem gives

A.

an equivalent current source in parallel with an equivalent impedance

B.

an equivalent current source in series with an equivalent impedance

C.

an equivalent voltage source in parallel with an equivalent impedance

D.

an equivalent voltage source in series with an equivalent impedance


Three-Phase Systems in Power Applications

1. In a three-phase system, the voltages are separated by

A.

45°

B.

90°

C.

120°

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D.

180°


2. In a three-phase system, when the loads are perfectly balanced, the neutral current is

A.

zero

B.

one-third of maximum

C.

two-thirds of maximum

D.

at maximum


3. In a -connected source driving a -connected load, the

A.

load voltage and line voltage are one-third the source voltage for a given phase

B.

load voltage and line voltage are two-thirds the source voltage for a given phase

C.

load voltage and line voltage cancel for a given phase

D.

load voltage, line voltage, and source phase voltage are all equal for a given phase


4. In a certain three-wire Y-connected generator, the phase voltages are 2 kV. The magnitudes of the line voltages are

A.

2,000 V

B.

6,000 V

C.

666 V

D.

3,464 V


5. In a -connected source feeding a Y-connected load,

A.

each phase voltage equals the difference of the corresponding load voltages

B.

each phase voltage equals the corresponding load voltage

C.

each phase voltage is one-third the corresponding load voltage

D.

each phase voltage is 60° out of phase with the corresponding load voltage


6. In a Y-Y source/load configuration, the

A.

phase current, the line current, and the load current are all equal in each phase

B.

phase current, the line current, and the load current are 120° out of phase

C.

phase current and the line current are in phase, and both are 120° out of phase with the load current

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D.

line current and the load current are in phase, and both are out of phase with the phase current


7. In a Y-connected circuit, the magnitude of each line current is

A.

one-third the phase current

B.

three times the corresponding phase current

C.

equal to the corresponding phase current

D.

zero


8. A constant load power means a uniform conversion of

A.

mechanical to electrical energy

B.

electrical to mechanical energy

C.

current to voltage

D.

voltage to current


9. A two-phase generator is connected to two 90

load resistors. Each coil generates 120 V ac. A common neutral line exists. How much current flows through the common neutral line?

A.

1.33 A

B.

1.88 A

C.

2.66 A

D.

1.77 A


10. A single-phase sinusoidal voltage of 120 V is connected to a 90

load. Current in the circuit is

A.

13.3 mA

B.

133 mA

C.

1.33 A

D.

6.2 A


11. A three-phase generator is connected to three 90 load resistors. Each coil generates 120 V ac. A common neutral line exists. How much current flows through the common neutral line?

A.

0 A

B.

1.33 A

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C.

3.99 A

D.

2.66 A


12. Compare the total copper cross sections in terms of current-carrying capacity for a single-phase and a three-phase 120 V system with effective load resistance of 15 .

A.

single-phase 32 A; three-phase 16 A

B.


C.


D.



13. If in a Y-connected ac generator, each phase voltage has a magnitude of 90 V

RMS each line voltage?

, what is the magnitude of

A.

0 V

B.

90 V

C.

156 V

D.

180 V


14. Polyphase generators produce simultaneous multiple sinusoidal voltages that are separated by

A.

certain constant phase angles

B.

certain constant frequencies

C.

certain constant voltages

D.

certain constant currents


15. In a balanced three-phase load, each phase has

A.

an equal amount of power

16. In a certain Y-Y system, the source phase currents each have a magnitude of 9 A. The magnitude of each load current for a balanced load condition is

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B.

one-third of total power

C.

two-thirds of total power

D.

a power consumption equal to


I

L

A.

3 A

B.

6 A

C.

9 A

D.

27 A


17. A three-phase -connected generator is driving a balanced load such that each phase current is 12 A in magnitude. When I θ a

= 12 30° A, what are the polar expressions for the other phase currents?

A.

I

θ b

= 12 150° A, I

θ c

= 12 –90° A

B.

I

θ b

= 12 120° A, I

θ c

= 12 30° A

C.

I

θ b

= 12 30° A, I

θ c

= 12 120° A

D.

I

θ b

= 12 90° A, I

θ c

= 12 90° A


18. In a Y-connected circuit, between each line voltage and the nearest phase voltage, there is a phase angle of

A.

0°

B.

30°

C.

60°

D.

120°


19. The most common type of ac motor is the

A.

single-phase induction motor

B.

two-phase induction motor

C.

three-phase induction motor

D.

two-phase squirrel-cage motor


20. In a Y-connected source feeding a -connected load,

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A.

each phase of the load has one-third of the full line voltage across it

B.

each phase of the load has two-thirds of the full line voltage across it

C.

each phase of the load has the full line voltage across it

D.

each phase of the load has a voltage across it equal to


21. In a -connected generator, all of the phase voltages are

A.

zero

B.

equal in magnitude

C.

one-third of total

D.

one-sixth of total


Voltage, Current and Resistance

1. Materials with lots of free electrons are called

A.

conductors

B.

insulators

C.

semiconductors

D.

filters


2. The unit of electrical charge is the

A.

coulomb

B.

joule

C.

volt

D.

watt


3. Current flows in a circuit when

A.

a switch is opened

B.

a switch is closed

C.

the switch is either open or closed

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D.

there is no voltage


4. The minimum resistance value for a blue, gray, red, silver resistor is

A.

612

B.

6,120

C.

6,800

D.

6,460


Explanation:

Because of 10% tolerance(last color silver), this resistance may vary 10% of 6800.

Minimum resistance value = 6800 - 680 = 6120

Maximum resistance value = 6800 + 680 = 7480

View Answer Discuss in Forum Workspace Report

5. The maximum resistance value for a brown, red, yellow, gold resistor is

A.

126,000

B.

126,600

C.

114,000

D.

132,000


6. Which of the following is not a type of energy source?

A.

generator

B.

rheostat

C.

solar cell

D.

battery


7. When placed close together, two positively charged materials will

A.

attract

B.

become neutral

C.

become negative

D.

repel


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8. The conductance of an 8 ohm resistance is

A.

12.5 mS

B.

8 mS

C.

12 S

D.

125 mS


9. Electrons in the outer orbit are called

A.

nuclei

B.

valences

C.

waves

D.

shells


10. A thermistor is a type of

A.

switch

B.

resistor

C.

battery

D.

power supply


11.

A two-terminal variable resistor is known as a

A.

potentiometer

B.

thermistor

C.

rheostat

D.

wiper


12. Eight-tenths coulomb passes a point in 4 s. The current in amperes is

A.

1.6 A

B.

16 A

C.

2 A

D.

0.2 A


13. When the current is 2.5 A, how many coulombs pass a point in 0.2 s?

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A.

12.5 C

B.

1.25 C

C.

0.5 C

D.

5 C


14. The colored bands for a 4,700 ohm resistor with a ten percent tolerance are

A.

yellow, violet, red, gold

B.

yellow, violet, orange, gold

C.

yellow, violet, red, silver

D.

orange, violet, red, silver


15. A material that does not allow current under normal conditions is a(n)

A.

insulator

B.

conductor

C.

semiconductor

D.

valence


16. The unit of electrical charge is the

A.

volt

B.

ampere

C.

joule

D.

coulomb


17. A multimeter measures

A.

current

B.

voltage

C.

resistance

D.

current, voltage, and resistance


18. If there is 6 A of current through the filament of a lamp, how many coulombs of charge move through the filament in 1.75 s?

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A.

10.5 C

B.

105 C

C.

3.4 C

D.

34 C


19. A wiper is the sliding contact in a

A.

switch

B.

photoconductive cell

C.

thermistor

D.

potentiometer


20. A neutral atom with an atomic number of five has how many electrons?

A.

1

B.

5

C.

none

D.

depends on the type of atom


21. A circuit breaker is a

A.

fuse

B.

switch

C.

resettable protective device

D.

resistor


22. An ammeter is an electrical instrument used to measure

A.

current

B.

voltage

C.

resistance

D.

none of the above


23. A red, red, orange, gold resistor has a nominal value of

A.

22,000

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B.

2,200

C.

22

D.

2.2


24. An ohmmeter is an instrument for measuring

A.

current

B.

voltage

C.

resistance

D.

wattage


25. The current in a given circuit is not to exceed 24 A. Which value of fuse is best?

A.

a fuse is not necessary

B.

10 A

C.

24 A

D.

20 A


Energy and Power

1. A 33 half-watt resistor and a 330 half-watt resistor are connected across a 12 V source.

Which one(s) will overheat?

A.

33

B.

330

C.

both resistors

D.

neither resistor


2. When the pointer of an analog ohmmeter reads close to zero, the resistor being measured is

A.

overheated

B.

shorted

C.

open

D.

reversed


3. In 0.025 W, there are

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A.

25 kW

B.

0.00025 mW

C.

2,500 µW

D.

25 mW


4. A certain appliance uses 350 W. If it is allowed to run continuously for 24 days, how many kilowatt-hours of energy does it consume?

A.

20.16 kWh

B.

201.6 kWh

C.

2.01 kWh

D.

8.4 kWh


5. A power supply produces a 0.6 W output with an input of 0.7 W. Its percentage of efficiency is

A.

8.57%

B.

42.85%

C.

4.28%

D.

85.7%


6. A given power supply is capable of providing 6 A for 3.5 h. Its ampere-hour rating is

A.

0.58 Ah

B.

2.1 Ah

C.

21 Ah

D.

58 Ah


7. A 15 V source is connected across a 12 resistor. How much energy is used in three minutes?

A.

938 Wh

B.

0.938 Wh

C.

56.25 Wh

D.

5.6 Wh


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8. At the end of a 14 day period, your utility bill shows that you have used 18 kWh. What is your average daily power?

A.

1.286 kWh

B.

12.85 kWh

C.

535 kWh

D.

252 kWh


9. A 120 resistor must carry a maximum current of 25 mA. Its rating should be at least

A.

4.8 W

B.

150 mW

C.

15 mW

D.

480 mW


10. If you used 400 W of power for 30 h, you have used

A.

1.3 kWh

B.

13.3 kWh

C.

1.2 kWh

D.

12 kWh


11. A 6 V battery is connected to a 300 load. Under these conditions, it is rated at 40 Ah. How long can it supply current to the load?

A.

1 h

B.

200 h

C.

2,000 h

D.

10 h


12. In 40 kW, there are

A.

0.4 mW

B.

40,000 W

C.

400 W

D.

5,000 W


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13. If you used 600 W of power for 60 h, you have used

A.

36 kWh

B.

3.6 kWh

C.

10 kWh

D.

1 kWh


14.

If it takes 400 ms to use 12,000 J of energy, the power is

A.

30 kW

B.

30 W

C.

3 W

D.

300 kW


15. How many watt-hours represent 65 W used for 18 h?

A.

11.7 Wh

B.

1,170 Wh

C.

11,700 Wh

D.

117,000 Wh


16. For 12 V and 40 mA, the power is

A.

480 mW

B.

0.480 W

C.

480,000 µW

D.

all of the above


17.

A 220 resistor dissipates 3 W. The voltage is

A.

73.3 V

B.

2.5 V

C.

25.7 V

D.

257 V


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18. A 3.3 k

resistor dissipates 0.25 W. The current is

A.

8.7 mA

B.

87 mA

C.

8.7 µA

D.

8.7 A


Explanation:

W = I 2 R

I = square root(W/R)

= square root( 0.25/(3.3x1000) )

= 0.0087038828

= 8.7 mA

19. A half-watt is equal to how many milliwatts?

A.

5,000 mW

B.

5 mW

C.

500 mW

D.

50 mW


20. Three hundred joules of energy are consumed in 15 s. The power is

A.

2,000 W

B.

2 W

C.

20 W

D.

200 W


21. The power rating of a carbon-composition resistor that is to handle up to 1.2 W should be

A.

2 W

B.

1 W

C.

5 W

D.

0.5 W


22. How much continuous current can be drawn from a 60 Ah battery for 14 h?

A.

42.8 A

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B.

428 A

C.

4.28 A

D.

4.2 A


23. A 75 load uses 2 W of power. The output voltage of the power supply is approximately

A.

120 V

B.

1.2 V

C.

12 V

D.

6 V


24. When the current through a 12 k

resistor is 8 mA, the power is

A.

7.68 mW

B.

768 mW

C.

7.68 W

D.

76.8 W


25. A 68

resistor is connected across the terminals of a 3 V battery. The power dissipation of the resistor is

A.

132 mW

B.

13.2 mW

C.

22.6 mW

D.

226 mW


Parallel Circuits

A.

55

B.

5.5

C.

50

D.

9


2. The total resistance of a parallel circuit is 50 . If the total current is 120 mA, the current through

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https://sites.google.com/site/sdmservice15/ the 270 resistor that makes up part of the parallel circuit is approximately

A.

22 mA

B.

120 mA

C.

220 mA

D.

50 mA


3. The currents into a junction flow along two paths. One current is 4 A and the other is 3 A. The total current out of the junction is

A.

1 A

B.

7 A

C.

unknown

D.

the larger of the two


4. When an additional resistor is connected across an existing parallel circuit, the total resistance

A.

remains the same

B.

decreases by the value of the added resistor

C.

increases by the value of the added resistor

D.

decreases


5. When a 1.6 k

resistor and a 120 resistor are connected in parallel, the total resistance is

A.

greater than 1.6 k

B.

greater than 120 but less than 1.6 k

C.

less than 120 but greater than 100

6.

D.

less than 100


If there are a total of 120 mA into a parallel circuit consisting of three branches, and two of the branch currents are 40 mA and 10 mA, the third branch current is

A.

50 mA

B.

70 mA

C.

120 mA

D.

40 mA


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7. Three lights are connected in parallel across a 120 volt source. If one light burns out,

A.

the remaining two will glow dimmer

B.

the remaining two will glow brighter

C.

the remaining two will not light

D.

the remaining two will glow with the same brightness as before


8. Four equal-value resistors are connected in parallel. Ten volts are applied across the parallel circuit and 2 mA are measured from the source. The value of each resistor is

A.

12.5

B.

200

C.

20 K

D.

50


Explanation:

10/(R/4) = 2 mA

40/R = 2 mA

R = 40/2 mA

= 40/0.002 A

= 20000 kohm (20 kohm)

9. A set of Christmas tree lights is connected in parallel across a 110 V source. The filament of each light bulb is 1.8 k . The current through each bulb is approximately

A.

610 mA

B.

18 mA

C.

110 mA

D.

61 mA


10. The power dissipation in each of four parallel branches is 1.2 W. The total power dissipation is

A.

1.2 W

B.

4.8 W

C.

0.3 W

D.

12 W


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11. A 470

resistor, a 220 resistor, and a 100 resistor are all in parallel. The total resistance is approximately

A.

790

B.

470

C.

60

D.

30


Explanation:

1/R = (1/470 + 1/220 + 1/100)

R = 59.98 ohm

12. Five light bulbs are connected in parallel across 110 V. Each bulb is rated at 200 W. The current through each bulb is approximately

A.

2.2 A

B.

137 mA

C.

1.8 A

D.

9.09 A


13. Four resistors of equal value are connected in parallel. If the total voltage is 15 V and the total resistance is

600 , the current through each parallel resistor is

A.

25 mA

B.

100 mA

C.

6.25 mA

D.

200 mA


14. Five 100

resistors are connected in parallel. If one resistor is removed, the total resistance is

A.

25

B.

500

C.

100

D.

20


Explanation:

1/R = 1/R1 + 1/R2 + 1/R3 + 1/R4

1/R = 1/100 + 1/100 + 100 + 1/100

1/R = 4/100

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1/R = 1/25

Therefore R = 25 ohm.

15. Four 8 speakers are connected in parallel to the output of an audio amplifier. If the maximum voltage to the speakers is 12 V, the amplifier must be able to deliver to the speakers

A.

18 W

B.

1.5 W

C.

48 W

D.

72 W


16. In a certain three-branch parallel circuit, R

1

has 12 mA through it, R

2

has 15 mA through it, and R

3

has 25 mA through it. After measuring a total of 27 mA, you can say that

A.

R

3

is open

B.

R

1

is open

C.

R

2

is open

D.

the circuit is operating properly


17. A sudden increase in the total current into a parallel circuit may indicate

A.

a drop in source voltage

B.

an open resistor

C.

an increase in source voltage

D.

either a drop in source voltage or an open resistor


18. The following currents are measured in the same direction in a three-branch parallel circuit: 200 mA, 340 mA, and 700 mA. The value of the current into the junction of these branches is

A.

200 mA

B.

540 mA

C.

1.24 A

D.

900 mA


19. The following resistors are in parallel across a voltage source: 220

, 470 , and 560 . The resistor with the least current is

A.

220

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B.

470

C.

560

D.

impossible to determine without knowing the voltage


20. Three 47 resistors are connected in parallel across a 110 volt source. The current drawn from the source is approximately

A.

2.3 A

B.

780 mA

C.

47 mA

D.

7.06 A


21. There is a total of 800 mA of current into four parallel resistors. The currents through three of the resistors are 40 mA, 70 mA, and 200 mA. The current through the fourth resistor is

A.

490 mA

B.

800 mA

C.

310 mA

D.

0 A


22. Four resistors are connected in parallel. Fifteen mA flows through resistor R.

If the second resistor is 2 R , the third resistor 3 R , and the fourth resistor 4 R , the total current in the circuit is

A.

60 mA

B.

15 mA

C.

135 mA

D.

31.25 mA


23. If one of the resistors in a parallel circuit is removed, the total resistance

A.

decreases

B.

increases

C.

remains the same

D.

doubles


24. Six resistors are in parallel. The two lowest-value resistors are both 1.2 k . The total resistance

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A.

is less than 6 k

B.

is greater than 1.2 k

C.

is less than 1.2 k

D.

is less than 600


25. In a five-branch parallel circuit, there are 12 mA of current in each branch. If one of the branches opens, the current in each of the other four branches is

A.

48 mA

B.

12 mA

C.

0 A

D.

3 mA


Circuit Theorems and Conversions

1. Find the Thevenin equivalent ( V

TH

and R

TH

) between terminals A and B of the circuit given below.

A.

4.16 V, 120

B.

41.6 V, 120

C.

4.16 V, 70

D.

41.67 V, 70


2. A certain current source has the values I

S source are

= 4 µA and R

S

= 1.2 M . The values for an equivalent voltage

A.

4.8

V, 1.2 M

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B.

1 V, 1.2 M

C.

4.8 V, 4.8 M

D.

4.8 V, 1.2 M


3. Find the total current through R

3

in the given circuit.

A.

7.3 mA

B.

5.5 mA

C.

12.8 mA

D.

1.8 mA


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4. A 680

load resistor, R

L

, is connected across a constant current source of 1.2 A. The internal source resistance, R

S

, is 12 k . The load current, R

L

, is

A.

0 A

B.

1.2 A

C.

114 mA

D.

1.14 A


5. Find the current through R

2

of the given circuit.

A.

30.7 mA

B.

104 mA

C.

74 mA

D.

134 mA


6. Determine I

N

for the circuit consisting of V

S

, R

1

, R

2

, and R

3

shown in the given circuit.

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A.

676 mA

B.

245 mA

C.

431 mA

D.

75 mA


7. A 120 V voltage source has a source resistance, R

S

, of 60 . The equivalent current source is

A.

2 A

B.

4 A

C.

200 mA

D.

400 mA


8. A 12 V source has an internal resistance of 90

. If a load resistance of 20 is connected to the voltage source, the load power, P

L

, is

A.

2.38 mW

B.

2.38 W

C.

238 mW

D.

23.8 W


9. In a two-source circuit, one source acting alone produces 12 mA through a given branch. The other source acting alone produces 10 mA in the opposite direction through the same branch. The actual current through the branch is

A.

22 mA

B.

12 mA

C.

10 mA

D.

2 mA


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10. Find the current through R

1

in the given circuit.

A.

0.16 A

B.

0.24 A

C.

0.2 A

D.

0.04 A


11. What is the Thevenin equivalent ( V

TH

and R

TH

) for the circuit given?

A.

6.4 V, 422

B.

6.4 V, 560

C.

6.4 V, 680

D.

30 V, 422


12. Referring to the given circuit, the voltage and current for the load resistor, R

L

, is

A.

450 mV, 4.5 mA

B.

4.50 V, 45 mA

C.

4.50 V, 4.5 mA

D.

450 mV, 45 mA


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13. Find the current in R

2

of the given circuit, using the superposition theorem.

A.

16.7 mA

B.

33.3 mA

C.

50 mA

D.

16.6 mA


14. A 470 R

L

is connected across a voltage source, V

S

, of 120 V. The source's internal resistance, R

S

, is 12

. What is the output voltage across the load?

A.

120 V

B.

0 V

C.

117 V

D.

12 V


15. A 2

R

L

is connected across a voltage source,

What is the output voltage across the load?

V

S

, of 110 V. The source's internal resistance is 24 .

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A.

8.5 V

B.

85 V

C.

0 V

D.

110 V


16. An 18 V source has an internal resistance of 70

. If a load resistance of 33 is connected to the voltage source, the load power, P

L

, is

A.

0 W

B.

1 W

C.

175 mW

D.

18 mW


17. A certain voltage source has the values

V

S source are

= 30 V and R

S

= 6 . The values for an equivalent current

A.

5 A, 6

B.

30 A, 6

C.

5 A, 30

D.

30 A, 5


18. A 120 load is connected across an ideal voltage source with V

S

= 12 V. The voltage across the load

A.

is 0 V

B.

is 12 V

C.

is 120 V

D.



19. Find the Norton circuit, that is, I

IN

and R

N

, for the circuit given below.

A.

478 mA, 12.8

B.

750 mA, 12.8

C.

478 mA, 6.8

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D.

750 mA, 6.8


20. A 120 load is connected across a voltage source with V

S load is

= 12 V and R

S

= 8 . The voltage across the

A.

11.25 V

B.

0 V

C.

12 V

D.

1.13 V


21. Find R

N

for the circuit given.

A.

34

B.

68

C.

120

D.

154


22. Referring to circuit given, if R

1

is changed to a 68 resistor, what will be the current through it?

A.

0.16 A

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B.

0.24 A

C.

0.2 A

D.

0.04 A


23. Find the Thevenin equivalent ( V

TH

and R

TH

) between terminals A and B of the circuit given.

A.

562 mV, 167

B.

5.62 V, 167

C.

5.62 V, 188

D.

562 mV, 188


24. Referring to the given circuit, determine V

TH across R

2

and R

3

.

and R

TH

if a 68 resistor is connected in parallel

A.

3.3 V, 148

B.

330 mV, 148

C.

3.3 V, 68

D.

330 mV, 68


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25. A 12 mA current source has an internal resistance, R

S

, of 1.2 k . The equivalent voltage source is

A.

144 V

B.

14.4 V

C.

7.2 V

D.

72 mV


Magnetism and Electromagnetism

1. When the speed at which a conductor is moved through a magnetic field is increased, the induced voltage

A.

increases

B.

decreases

C.

remains constant

D.

reaches zero


2. The induced voltage across a coil with 250 turns that is located in a magnetic field that is changing at a rate of

8 Wb/s is

A.

1,000 V

B.

2,000 V

C.

31.25 V

D.

3,125 V


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3. For a given wirewound core, an increase in current through the coil

A.

reverses the flux lines

B decreases the flux density

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C.

increases the flux density

D.

causes no change in flux density


4. If the cross-sectional area of a magnetic field increases, but the flux remains the same, the flux density

A.

increases

B.

decreases

C.

remains the same

D.

doubles


5. When the current through the coil of an electromagnet reverses, the

A.

direction of the magnetic field reverses

B.

direction of the magnetic field remains unchanged

C.

magnetic field expands

D.

magnetic field collapses


6. What is the reluctance of a material that has a length of 0.07 m, a cross-sectional area of 0.014 m 2 , and a permeability of 4,500 Wb/At × m?

A.

1111 At/Wb

B.

111 At/Wb

C.

11 At/Wb

D.

1 At/Wb


7. A coil of wire is placed in a changing magnetic field. If the number of turns in the coil is decreased, the voltage induced across the coil will

A.

increase

B.

decrease

C.

remain constant

D.

be excessive


8. What is the flux density when the flux is 5.5

Wb and the cross-sectional area is 6 × 10 –3 m 2 ?

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A.

91.7 T

B.

917

T

C.

91 T

D.

9.7 T


9. The unit for reluctance is

A.

tesla

B.

At/Wb

C.

At/m

D.

Wb


10. If the steel disk in a crankshaft position sensor has stopped with the tab in the magnet's air gap, the induced voltage

A.

increases

B.

decreases

C.

is zero

D.

will remain constant


11. There is 900 mA of current through a wire with 40 turns. What is the reluctance of the circuit if the flux is 400

Wb?

A.

14,400 At/Wb

B.

1,440 At/Wb

C.

9,000 At/Wb

D.

90,000 At/Wb


12. A basic one-loop dc generator is rotated at 90 rev/s. How many times each second does the dc output voltage peak (reach maximum)?

A.

90

B.

180

C.

270

D.

360


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13. What is the flux density in a magnetic field in which the flux in 0.1 m

2 is 600 Wb?

A.

6,000 T

B.

600 T

C.

600 T

D.

6 T


14. The unit for permeability is

A.

Wb/At × m

B.

At/m

C.

At/Wb

D.

Wb


15. What is the magnetomotive force in a 75-turn coil of wire when there are 4 A of current through it?

A.

18.75 At

B.

30 At

C.

300 At

D.

187 At


16. The direction of a magnetic field within a magnet is

A.

from south to north

B.

from north to south

C.

back to front

D.

front to back


17. When the north poles of two bar magnets are brought close together, there will be

A.

no force

B.

a downward force

C.

a force of attraction

D.

a force of repulsion


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18. The ability of a material to remain magnetized after removal of the magnetizing force is known as

A.

permeability

B.

reluctance

C.

hysteresis

D.

retentivity


19. The voltage induced across a certain coil is 200 mV. A 120

resistor is connected to the coil terminals.

The induced current is

A.

1.7 mA

B.

16 mA

C.

12 mA

D.

120 mA


20. The induced voltage across a stationary conductor in a stationary magnetic field is

A.

zero

B.

reversed in polarity

C.

increased

D.

decreased


21. An electromagnetic field exists only when there is

A.

an increasing current

B.

decreasing current

C.

voltage

D.

current


22. When a solenoid is activated, the force that moves the plunger is

A.

an electromagnetic field

B.

a permanent magnetic field

C.

varying voltage

D.

a steady current


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23. What is the magnetomotive force (mmf) of a wire with 8 turns carrying three amperes of current?

A.

2,400 At

B.

240 At

C.

24 At

D.

2.4 At


24. If a loop in a basic dc generator suddenly begins rotating at a faster speed, the induced voltage

A.

remains unchanged

B.

reverses polarity

C.

increases

D.

decreases


Capacitors

1. A 10

F, 20 F, 22 F, and 100 F capacitor are in parallel. The total capacitance is

A.

2.43 F

B.

4.86 F

C.

100 F

D.

152 F


2. A capacitor and a resistor are connected in series to a sine wave generator. The frequency is set so that the capacitive reactance is equal to the resistance and, thus, an equal amount of voltage appears across each component. If the frequency is increased

A.

V

R

> V

C

B.

V

C

> V

R

C.

V

R

= V

C

D.

V

R

and V

C

= 0


3. A capacitor of 0.02

F is larger than

A.

0.000020 F

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B.

200,000 pF

C.

2,000 pF

D.

all of the above


4. In Question 6, the capacitor will reach full charge in a time equal to approximately

A.

6 RC

B.

5 RC

C.

RC

D.

none of the above


5. What is the capacitance when

Q = 60 C and V = 12 V?

A.

720 F

B.

5 F

C.

50 F

D.

12 F


6. A 0.47

F capacitor is across a 2 kHz sine wave signal source. The capacitive reactance is

A.

170

B.

17

C.

0.000169

D.

1.7


7. Four 0.15

F capacitors are in parallel. The total capacitance is

A.

0.15 F

B.

0.30 F

C.

0.6 F

D.

0.8

F


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8. Which of the following capacitors is polarized?

A.

mica

B.

ceramic

C.

plastic-film

D.

electrolytic


9. A capacitor of 2,000 pF is greater than

A.

0.02

F

B.

0.002 F

C.

0.0002

F

D.

0.0000002 F


10. A 220 resistor is in series with a 2.2

F capacitor. The time constant is

A.

48 s

B.

480 s

C.

2.42 s

D.

24 s


11. A 4.7 M resistor is in series with a 0.015 long does it take the capacitor to fully charge?

F capacitor. The combination is across a 12 V source. How

A.

35 ms

B.

352 ms

C.

3.5 s

D.

70.5 ms


12. A sine wave voltage is applied across a capacitor. When the frequency of the voltage is decreased, the current

A.

increases

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B.

remains constant

C.

decreases

D.

ceases


13. Of the following capacitors, which one has the highest dielectric constant?

A.

air

B.

mica

C.

glass

D.

paper


14. A 0.01

F capacitor equals how many picofarads?

A.

100 pF

B.

1,000 pF

C.

10,000 pF

D.

100,000 pF


15. A 12 kHz voltage is applied to a 0.33 value of the voltage?

F capacitor, and 200 mA of rms current is measured. What is the

A.

8 V

B.

80 V

C.

80 mV

D.

800 mV


16. A 0.00022 F capacitor equals how many microfarads?

A.

22 F

B.

220 F

C.

2,200

F

D.

22,200 F


17. Two series capacitors (one 2

F, the other of unknown value) are charged from a 24 V source. The 2

F capacitor is charged to 16 V and the other to 8 V. The value of the unknown capacitor is

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A.

1 F

B.

2

F

C.

4 F

D.

8 F


18. A 330 pF capacitor and a 220 pF capacitor are each connected across a 6 V dc source. The voltage across the 330 pF capacitor is

A.

3 V

B.

6 V

C.

4 V

D.

0 V


19. A 2

F, a 4 F, and a 10 F capacitor are connected in series. The total capacitance is less than

A.

2

F

B.

4 F

C.

10

F

D.

1.5 F


20. When the plate area of a capacitor increases,

A.

the capacitance increases

B.

the capacitance decreases

C.

the capacitance is unaffected

D.

the voltage it can withstand increases.


21. Two 0.68

F capacitors are connected in series across a 10 kHz sine wave signal source. The total capacitive reactance is

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A.

46.8

B.

4.68

C.

23.41

D.

11.70


22. An uncharged capacitor and a 1 k

resistor are connected in series with a switch and a 6 V battery. At the instant the switch is closed, the voltage across the capacitor is

A.

6 V

B.

3 V

C.

2 V

D.

0 V


23. When the voltage across a capacitor is tripled, the stored charge

A.

triples

B.

is cut to one-third

C.

stays the same

D.

doubles


Transformers

1. What kVA rating is required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV?

A.

4 kVA

B.

0.25 kVA

C.

16 kVA

D.

8 kVA


2. The turns ratio required to match an 80

source to a 320 load is

A.

80

B.

20

C.

4

D.

2

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3. When the turns ratio of a transformer is 20 and the primary ac voltage is 12 V, the secondary voltage is

A.

12 V

B.

120 V

C.

240 V

D.

2,400 V


4. If a transformer has 50 turns in the primary winding and 10 turns in the secondary winding, what is the reflective resistance if the secondary load resistance is 250 ?

A.

250

B.

25

C.

6,250

D.

62,500


5. A certain transformer has 400 turns in the primary winding and 2,000 turns in the secondary winding. The turns ratio is

A.

0.2

B.

0.4

C.

5

D.

25


6. The primary winding of a transformer has 110 V ac across it. What is the secondary voltage if the turns ratio is 8?

A.

8.8 V

B.

88 V

C.

880 V

D.

8,800 V


Explanation:

V2/V1 = N2/N1

Turns ratio = N2/N1 = 8.

V2/110 = 8

V2 = 8 x 110

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V2 = 880v.

7. To step 110 V ac down to 20 V ac, the turns ratio must be

A.

5.5

B.

18

C.

0.18

D.

0.018


Explanation:

Vp/Vs = Np/Ns

Vs = (Ns/Np)Vp

We required turns ratio i.e., (Ns/Np)

= Vs/Vp

= 20/110

= 0.181818182

[Note: p - primary; s - secondary]

For step down transfer, the turns ratio will be less than 1.

8. The mutual inductance when k = 0.65, L

1

= 2 H, and L

2

= 5 H is

A.

2 mH

B.

2

H

C.

4 H

D.

8 H


9. If 25 W of power are applied to the primary of an ideal transformer with a turns ratio of 10, the power delivered to the secondary load is

A.

25 W

B.

0 W

C.

250 W

D.

2.5 W


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10. A transformer with a 110 V primary has a 15:1 turns ratio. The load resistance,

R

L approximate voltage across the load?

, is 120 . What is the

A.

7.3 V

B.

73 V

C.

88 V

D.

880 V


11. 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


Explanation:

We know that, V2/V1 = N2/N1.

Given V2 = 9v, N2/N1 = 0.1

Therefore, 9v/V1 = 0.1

V1 = 9v/0.1 = 90v.

12. 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


13. 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


14. 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?

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A.

2 V

B.

20 V

C.

180 V

D.

18 V


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

A.

open

B.

shorted

C.

switched

D.

fused


16. 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


17. 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


18. The primary of a transformer is connected to a 6 V battery. The turns ratio is 1:3 and the secondary load, R

L

, is 100 . The voltage across the load is

A.

0 V

B.

6 V

C.

18 V

D.

2 V


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19. 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


20. 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


21. 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


22. 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


23. 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

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C.

9.6

D.

0.96


24. 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


RL Circuits

1. A 1.5 k resistor and a coil with a 2.2 k inductive reactance are in series across an 18 V ac source. The power factor is

A.

564

B.

0.564

C.

6.76

D.

55.7


2. The voltages in Problem 5 are measured at a certain frequency. To make the resistor voltage less than the inductor voltage, the frequency is

A.

increased

B.

decreased

C.

doubled

D.

not a factor


3. In a series RL circuit, 12 V rms is measured across the resistor, and 14 V rms is measured across the inductor. The peak value of the source voltage is

A.

18.4 V

B.

26.0 V

C.

2 V

D.

20 V


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4. Referring to Problem 18, the circuit impedance is

A.

458 –76°

B.

4.58 –76°

C.

458 76°

D.

4.58

76°


5. To increase the current in a series RL circuit, the frequency

A.

should be increased

B.

should be decreased

C.

should be constant

D.



6. A 470 resistor and a coil with 125 inductive reactance are in parallel. Both components are across a

15 V ac voltage source. Current through the inductor is

A.

152 mA

B.

32 mA

C.

12 mA

D.

120 mA


7. A 1.2 k resistor is in series with a 15 mH coil across a 10 kHz ac source. The magnitude of the total impedance is

A.

152.6

B.

1,526

C.

1,200

D.

942


8. When the frequency is decreased, the impedance of a parallel RL circuit

A.

increases

B.

decreases

C.

remains constant

D.

is not a factor

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9. A 470

resistor and a 200 mH coil are in parallel. Both components are across a 1.5 kHz ac source. The total admittance of the circuit, in polar form, is

A.

12.60 –76° mS

B.

12.18

76° mS

C.

218 –76° mS

D.

12.18 –76° mS


10. Referring to Problem 23, the reactive power is

A.

10 mVAR

B.

100 mVAR

C.

6.76 mVAR

D.

148 mVAR


11. A 12 k

resistor is in series with a 90 mH coil across an 8 kHz ac source. Current flow in the circuit, expressed in polar form, is I = 0.3

0° mA. The source voltage, expressed in polar form, is

A.

3.84

20.6° V

B.

12.8

20.6° V

C.

0.3

20.6° V

D.

13.84

69.4° V


12. A 140

resistor is in parallel with an inductor having 60 inductive reactance. Both components are across a 12 V ac source. The magnitude of the total impedance is

A.

5.51

B.

55.15

C.

90

D.

200


13. When the frequency of the voltage applied to a series RL circuit is decreased, the impedance

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A.

decreases

B.

increases

C.

does not change

D.



14. In a parallel RL circuit, there are 3 A rms in the resistive branch and 3 A rms in the inductive branch. The total rms current is

A.

6 A

B.

424 mA

C.

4.24 A

D.

42.4 A


15. A 47 resistor is in series with an inductive reactance of 120 across an ac source. The impedance, expressed in polar form, is

A.

47 68.6°

B.

120 68.6°

C.

129 31.4°

D.

129 68.6°


16. When the resistor voltage in a series RL circuit becomes less than the inductor voltage, the phase angle

A.

increases

B.

decreases

C.

is not affected

D.



17. Which of the following power factors results in less energy loss in an RL circuit?

A.

1

B.

0.8

C.

0.4

D.

0.2


18. Referring to Problem 20,

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A.

the applied voltage lags the current

B.

the current lags the applied voltage

C.

the applied voltage and the current are in phase

D.

the current lags the applied voltage by 90°


19. A 3.3 k resistor and a 120 mH coil are in parallel. Both components are across a 2 kHz, 12 V ac source.

The total current in the circuit is

A.

8.74 mA

B.

874 mA

C.

874 A

D.

8.74

A


20. When the frequency of the voltage applied to a series RL circuit is increased, the phase angle

A.

decreases

B.

increases

C.

does not change

D.



21. If a load is purely inductive and the reactive power is 12 VAR, the apparent power is

A.

0 VA

B.

12 VA

C.

6 VA

D.

24 VA


22. If the frequency is halved and the resistance is doubled, the impedance of a series RL circuit

A.

doubles

B.

halves

C.

remains constant

D.



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Passive Filters

1. In a certain parallel resonant band-pass filter, the resonant frequency is 14 kHz. If the bandwidth is 4 kHz, the lower frequency

A.

is 7 kHz

B.

is 10 kHz

C.

is 12 kHz

D.



2. An RL low-pass filter consists of a 5.6 mH coil and a 3.3 k resistor. The output voltage is taken across the resistor. The circuit's critical frequency is

A.

93.8 kHz

B.

93.8 Hz

C.

861 Hz

D.

86.12 kHz


3. In a series resonant band-pass filter, a lower value of Q results in

A.

a higher resonant frequency

B.

a smaller bandwidth

C.

a higher impedance

D.

a larger bandwidth


4. The maximum output voltage of a certain low-pass filter is 15 V. The output voltage at the critical frequency is

A.

0 V

B.

15 V

C.

10.60 V

D.

21.21 V


5. A parallel resonant band-pass filter consists of a 90

resistor in series with a parallel network made up of a 60 mH coil and a 0.02 F capacitor. The output is taken across the capacitor/coil. The coil winding has a resistance of 20 . What is the center frequency of the filter?

A.

459 Hz

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B.

4,591 Hz

C.

999 Hz

D.

2,176 Hz


6. An RL high-pass filter consists of a 470 resistor and a 600 mH coil. The output is taken across the coil.

The circuit's critical frequency is

A.

125 Hz

B.

1,250 Hz

C.

564 Hz

D.

5,644 Hz


7. Referring to Problem 23, what will the output voltage be if the coil's internal resistance is neglected?

A.

0 V

B.

200 mV

C.

11.1 mV

D.

111 mV


8. A parallel resonant band-pass filter consists of a 6.8

resistor in series with a parallel network made up of an 8 H coil and a 120 pF capacitor. The output is taken across the capacitor/coil. Assume R

W

What is the center frequency of the filter?

= 0 .

A.

5.14 MHz

B.

514 kHz

C.

5.03 MHz

D.

503 kHz


9. A series resonant band-pass filter consists of a 2 mH coil, a 0.005

F capacitor, and a 120 resistor.

The winding resistance of the coil is 12 . The output voltage is taken off the resistor. Input voltage is 12

V rms

. What is the output voltage magnitude at the center frequency ( f

0

)?

A.

10.9 V

B.

1.09 V

C.

1.1 V

D.

12 V


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10. The same signal in Problem 2 is applied to an RC high-pass filter. If the reactance is zero at the input frequency, the output voltage is

A.

18 V peak-to-peak

B.

zero

C.

9 V peak-to-peak

D.

12.73 V peak-to-peak


11. An

RC low-pass filter consists of a 120 resistor and a 0.002 F capacitor. The output is taken across the capacitor. The circuit's critical frequency is

A.

333 kHz

B.

633 kHz

C.

331 kHz

D.

60 kHz


12. Referring to Problem 8, assume the input voltage is 15 V ac. What is the output voltage at the critical frequency, f c

?

A.

0 V

B.

7.07 V

C.

15 V

D.

10.6 V


13. Referring to Problem 21, the filter's bandwidth is

A.

11.5 Hz

B.

530 Hz

C.

53 Hz

D.

106 Hz


14. Referring to Problem 15, if the input voltage is a 6 V sine wave with a dc level of 10 V, what is the output voltage magnitude?

A.

6 V

B.

597 mV

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C.

5.97 V

D.

0 V


15. In a certain low-pass filter, f c

= 3.5 kHz. Its passband is

A.

0 Hz to 3.5 kHz

B.

0 Hz

C.

3.5 kHz

D.

7 kHz


16. An RC high-pass filter consists of an 820 resistor. What is the value of C so that X c than R at an input frequency of 12 kHz?

is ten times less

A.

81

F

B.

161 F

C.

0.161 F

D.

220 F


17. A series resonant band-stop filter consists of a 68 resistor, a 110 mH coil, and a 0.02

F capacitor.

The internal resistance, R

W

, of the coil is 4 . Input voltage is 200 mV. Output voltage is taken across the coil and capacitor in series. What is the output voltage magnitude at f

0

?

A.

1.1 mV

B.

11.1 mV

C.

111 mV

D.

200 mV


18. A sinusoidal voltage with a peak-to-peak value of 18 V is applied to an RC low-pass filter. If the reactance at the input frequency is zero, the output voltage is

A.

18 V peak-to-peak

B.

zero

C.

9 V peak-to-peak

D.

12.74 V peak-to-peak


19. V out

= 500 mV, and V in

= 1.3 V. The ratio V out

/ V in

expressed in dB is

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A.

0 dB

B.

8.30 dB

C.

–8.30 dB

D.

0.8 dB


20. Referring to Problem 8, assume the input voltage is 15 V dc. What is the output voltage?

A.

0 V

B.

15 V

C.

7.07 V

D.

10.6 V


21. At a certain frequency, the output voltage of a filter is 6 V and the input is 12 V. The voltage ratio in decibels is

A.

6.02 dB

B.

–6.02 dB

C.

12.04 dB

D.

–12.04 dB


22. An

RC high-pass filter consists of a 0.2 F capacitor and a 220 resistor. The output is taken across the resistor. The circuit's critical frequency is

A.

723 Hz

B.

7,234 Hz

C.

362 Hz

D.

3,617 Hz


Time Response of Reactive Circuits

1. When a 15 V input pulse with a width equal to two time constants is applied to an RC integrator, the capacitor charges to

A.

15 V

B.

12.9 V

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C.

8.6 V

D.

19.45 V


2. An integrator consists of a 3.3 k resistor and a 2 the input. How much will the capacitor charge?

F capacitor. A single 30 V, 6 ms pulse is applied to

A.

10.3 V

B.

30 V

C.

12.09 V

D.

17.91 V


3. Referring to Problem 5, how long will it take the capacitor to discharge if the internal resistance of the pulse source is 100 ?

A.

300 s

B.

600 s

C.

900 s

D.

1.5 ms


4. With an RL integrator, at the instant of the rising pulse edge,

A.

all the input voltage is across the resistor

B.

all the input voltage is across the inductor

C.

63 percent of the input voltage is across the resistor

D.

63 percent of the input voltage is across the inductor


5. When a 12 V input pulse with a width equal to one time constant is applied to an RC integrator, the capacitor charges to

A.

0 V

B.

12 V

C.

6.3 V

D.

7.56 V


6. Referring this circuit, determine the maximum output voltage when a single pulse is applied as shown. The total resistance is 60 .

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A.

2.73 V

B.

27.33 V

C.

30 V

D.

2.67 V


7. A steady-state condition is reached when

A.

the output voltage reaches the average value of the input voltage

B.

the output voltage reaches the input voltage

C.

the output voltage reaches approximately 63% of the input voltage

D.

the output voltage reaches the effective value of the input voltage


8. Referring to the give circuit, the output will

A.

decay to zero at the end of the pulse

B.

reach 6 V at the end of the pulse

C.

reach 3.78 V at the end of the pulse

D.

reach 5.16 V at the end of the pulse


9. A single 6 V pulse with a width of 600 s is applied to an integrator consisting of a 150 k resistor and a

0.002 F capacitor. To what voltage will the capacitor charge?

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A.

0 V

B.

3.78 V

C.

5.16 V

D.

6 V


10. To understand how the output voltage is shaped by a differentiator, you must consider

A.

the response to the rising pulse edge

B.

the response between the rising and falling edges

C.

the response to the falling pulse edge

D.

all of the above


11. If the capacitor in an integrator becomes leaky,

A.

the time constant will be effectively reduced

B.

the waveshape of the output voltage across C is altered

C.

the amplitude of the output is reduced

D.

all of the above


12. Referring to the above figure, determine the voltage level that the output will reach during the pulse.

A.

0 V

B.

15 V

C.

6.3 V

D.

9.45 V


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13. An RC differentiator acts as a

A.

low-pass filter

B.

high-pass filter

C.

band-pass filter

D.

band-stop filter


14. In an RL differentiator, when the input pulse goes from its low level to its high level,

A.

the inductor prevents a sudden change in voltage

B.

the inductor prevents a sudden change in current

C.

voltage across the inductor instantly reaches 63% of input voltage

D.

voltage across the inductor is zero


15. Referring this figure, on the falling edge,

A.

the resistor voltage drops to –5 V and then goes back to zero exponentially

B.

the resistor voltage jumps to –5 V and then goes back to zero exponentially

C.

the capacitor voltage remains constant

D.

the resistor voltage jumps to +5 V and then decreases exponentially to zero


16. In an RC differentiator, responding to repetitive pulses, the average value of the output

A.

is zero

B.

is equal to the input voltage

C.

is 63 percent of the input voltage

D.



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17. The output of an RC integrator is taken across the

A.

diode

B.

capacitor

C.

resistor

D.

source


18. In an RC differentiator, the sum of the capacitor voltage and the resistor voltage at any instant

A.

must be zero

B.

must be equal to the applied voltage

C.

is less than the applied voltage but greater than zero

D.



19. When a 24 V input pulse with a width equal to five time constants is applied to an RC integrator, the capacitor charges to

A.

24 V

B.

15.12 V

C.

20.64 V

D.

12 V


20. If the RC time constant of an integrator is increased, as the time constant is increased

A.

the capacitor charges more during a pulse and discharges less between pulses

B.

the capacitor charges less during a pulse and discharges more between pulses

C.

the capacitor charges more during a pulse and discharges more between pulses

D.

the capacitor charges less during a pulse and discharges less between pulses


21. If a periodic pulse waveform has a pulse width and the time between pulses each equal to or greater than five time constants, the capacitor will

A.

partially charge and fully discharge during each period of the input waveform

B.

fully charge and partially discharge during each period of the input waveform

C.

fully charge and fully discharge during each period of the input waveform

D.

partially charge and partially discharge during each period of the input waveform


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22. What is the highest frequency contained in a pulse that has a rise and fall time equal to 10 microseconds

(10 s)?

A.

35 kHz

B.

3.5 kHz

C.

10 kHz

D.

100 kHz


23. Referring to Problem 7, how much will the capacitor charge if the pulse width is increased to 12 ms?

A.

2.51 V

B.

25.14 V

C.

4.86 V

D.

12.76 V


24. In electronic systems, repetitive-pulse waveforms are encountered

A.

more often than single pulses

B.

less often than single pulses

C.

about as often as single pulses

D.

twice as often as single pulses


25. In an RC differentiator, the capacitor

A.

charges exponentially at a rate depending on the RC time constant

B.

charges exponentially at a rate depending on the input voltage

C.

charges when the input voltage is decreasing

D.

charges to approximately one time constant


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369587509-Quiz-Question-and-answers-for-Electrical-docx

For quantities and units

Ohm's Law

Series Circuits

Series-Parallel Circuits

Branch, Loop and Node Analyses

Alternating Current and Voltage

Inductors

RC Circuits

RLC Circuits and Resonance

Circuit Theorems in AC Analysis

Three-Phase Systems in Power Applications

Voltage, Current and Resistance

Energy and Power

Parallel Circuits

Circuit Theorems and Conversions

Magnetism and Electromagnetism

Capacitors

Transformers

RL Circuits

Passive Filters

Time Response of Reactive Circuits

Related documents

Products

Support

369587509-Quiz-Question-and-answers-for-Electrical-docx

For quantities and units

Ohm's Law

Series Circuits

Series-Parallel Circuits

Branch, Loop and Node Analyses

Alternating Current and Voltage

Inductors

RC Circuits

RLC Circuits and Resonance

Circuit Theorems in AC Analysis

Three-Phase Systems in Power Applications

Voltage, Current and Resistance

Energy and Power

Parallel Circuits

Circuit Theorems and Conversions

Magnetism and Electromagnetism

Capacitors

Transformers

RL Circuits

Passive Filters

Time Response of Reactive Circuits

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