Electricity CPUs Ethics Solutions

Electrical; Computers; Ethics

Workshop Solutions

Spring 2013

1Workshop Notes

FE Electrical General

Problem and Solution Set

2Introduction Problems and Solutions

I. Electrical Circuits

Problems 1-35, Pages 4-41 II. Computers

Problems 1-18, Pages 43-60

III. Ethics

Problems 1-28, Pages 62-93

3Electrical Circuits

Problems and Solutions

4Workshop Notes

Problem 1

What is the exerted force on the center charge for the system of three collinear charges X, Y, and Z? Solutions: Therefore, There is no force on the center charge Y. The correct answer is (A).

Qx = 2C, QY = 2C, QZ = 8C. Assume = 8.85 x 10 F/m

X Y Z

4 m

6 m

4 m

6 m

X Y Z Fx Fz

N 0(4)4

8 x 24)-(642 2

22

xFY

Page 193 from Supplied Reference Handbook

5Workshop Notes

Problem 2 A point X with coordinates (10, 12.25) carrying a 10 C charge is separated by air from point Y (10.25, 12) carrying a 20 C charge. What is the force between them? Solution: The correct answer is (B).

FY FX Qx 10C 20C QY

X (10, 12.25) Y (10.25, 12)

Page 22 and 193 from Supplied Reference Handbook

6Workshop Notes

Problem 3 An electric point charge of Q = 5 x 10 C is placed in a vacuum. If the permittivity of free space is 8.854 x 10 F/m, the field strength at a distance of 1m from the charge is approximately (A) 1.2 x 10 V/m (B) 4.5 x 10 V/m (C) 12 x 10 V/m (D) 15 x 10 V/m Solution: The electric field strength, E, at a distance r from the charge Q is given by The correct answer is (B).

V/m 10 x 5.4m) 10 x 1)(/10 x )(8.854(4

C 10 x 5

4

1226-12-

10-

20

mFE

rQE


7Workshop Notes

Problem 4 What is the work required to move a positive charge of 10C for a distance of 5m in the same direction as a uniform field of 50 V/m? Solution: The work required to move a charge in a uniform field is: The positive charge moves in the direction of the field; thus, no external work is required, and the charge returns potential energy to the field. The correct answer is (A).


QEdLdEQWp

p

1

2

8Workshop Notes

Problem 5 A coil with an inductance of 11 mH has a current of 5mA passing through it. The magnetic energy stored in the coil is most nearly (A) 0.14 J (B) 0.55 J (C) 1.6 J (D) 5.6 J Solution: The magnetic energy, U, stored in a conductor whose inductance is L and current is I is The correct answer is (A).

J) (0.14 J 10 x 375.1

A) 10 x H)(5 10 x 11(21

21

7-

23-3-

2

U

U

LIU


9Workshop Notes

Problem 6 A particle with a charge of Q = 1.6 x 10 C is to be moved between points A and B. The points have a potential difference between them of VAB = 3000 V. The work required to move the charge is (A) - 4.8 x 10 J (B) - 4.8 x 10 J (C) - 16 x 10 J (D) - 20 x 10 J Solution: The work, W, required is given by W = - QVAB W = - (1.6 x 10 C)(3000 V) W = - 4.8 x 10 J The correct answer is (B).

10

Workshop Notes

Problem 7 A conductor with a length of 0.4m carrying a current I is placed in a magnetic field with magnetic flux density of 0.01 T. The field and current direction are orthogonal. If the field exerts a force of 2 x 10 N on the conductor, the current in the conductor is most nearly (A) 1.0 A (B) 5.0 A (C) 10 A (D) 15 A Solution: The force exerted by the field on the conductor is the product of the current, length, and magnetic flux density. The correct answer is (B).

A 0.5T) 1(0.4m)(0.0

N 10 x 2 2-

LBFI

ILBF


11

Workshop Notes

Problem 8 A square metal plate with a 30 cm width carries 12 C. What is the electric field 2 cm away from the center of the plate? Solution:

The correct answer is C.

12

Workshop Notes

Problem 9 A conductor at 20C has a resistivity = 1.77 x m. The conductor is 1,000 m long and is 1mm in diameter. What is the resistance of the conductor? Solution:

The correct answer is B.


Area = r = (/4)d

A.

A. 20.5 Ohms

B. 22.5 Ohms

C. 2.25 Ohms

D. 2.50 Ohms

13

Workshop Notes

Problem 10

A. 0.32 B. 0.38 C. 0.26 D. 0.43

The correct answer is C.


14

Workshop Notes

Problem 11 An electric heater consists of two resistors in series. At 20C, they have resistances of 300 and 150 , and average temperature coefficients of 0.001/C and 0.004/C respectively. What is most nearly the total resistance at 50C?


15

Workshop Notes

Problem 11/Contd.


16

Workshop Notes

Problem 12

What is the voltage across the R2 resistor (1) in the following circuit? A. 10V B. 5V C. 15V D. 1V Solution: Using Kirchoffs Voltage Law: Thus, the correct answer is (A).

VAVAAAIII

RIV

R

R

10)1(1010100

)2(

2

21

2

17

Workshop Notes

Problem 13 Find the currents through the following schematic? Solution:

10 V

R2

8 +

+

Eq. 1

Eq. 2

The correct answer is (D).

18

Workshop Notes

Problem 14 Determine the current I and its direction from the following illustration. Solution:

The correct answer is (B).

19

Workshop Notes

Problem 15

The correct answer is A.


20

Workshop Notes

Problem 16 What is the voltage across the 4 resistor R3 in the following circuit? Solution: Find the equivalent resistance and voltage: The correct answer is (B).

21

Workshop Notes

Problem 17 What is the equivalent resistance of the circuit? A. 3.50 B. 2.54 C. 2.37 D. 3.67 Solution: The correct answer is (C). Page 194 from Supplied Reference Handbook

22

Workshop Notes

Problem 18 What is the current I out of the battery for this circuit? A. 15.33 A B. 20.12 A C. 16.88 A D. 17.67 A Solution: From the previous problem: Req = 2.37 The correct answer is (C).

I

23

Workshop Notes

Problem 19 A 2 resistor observes a 2A current for 2 seconds followed by a 4A current for another 2 seconds. What is the energy produced by the resistor over the 4 second time interval above?


24

Workshop Notes

Problem 19/Contd.


25

Workshop Notes

Problem 20 Find the Thevenin equivalent resistance and voltage at AB in the following schematic. Solution: To find the Thevenin equivalent resistance we short circuit the power source. Therefore, R1 is bypassed or shorted.

IR3 VTH

The correct answer is (D).

26

Workshop Notes

Problem 21 What are the Norton equivalent current source and resistance values for the circuit shown? A. In = 2 A, RN = 15 B. In = 1 A, RN = 15 C. In = 2 A, RN = 3.33 D. In = 1 A, RN = 3.33 Solution: To find RN, the voltage source is shorted; then, the short circuit current is measured through terminals AB. Thus, R1 is bypassed or shorted. The correct answer is (C).

ISC

27

Workshop Notes

Problem 22 What is the equivalent capacitance of the circuit shown? Solution: The correct answer is (B). Page 195 from Supplied Reference Handbook

28

Workshop Notes

Problem 23


29

Workshop Notes

Problem 24 What is the equivalent inductance for the circuit shown? Solution: The correct answer is (B).

30

Workshop Notes

Problem 25 What is the DC current through the inductor in the following circuit?


31

Workshop Notes

Problem 26 If the current flowing through the circuit is 10A, what is the total energy stored in the circuit inductors?

10A

The correct answer is D.


32

Workshop Notes

Problem 27 What is the effective current in the graph shown? A. 50 A B. 35.36 A C. 25 A D. 0 A Solution: The rms value is calculated form the peak value. The correct answer is B.


AAII MAXRMS 36.35250

2

33

Workshop Notes

Problem 28 What is the resonant frequency of the circuit shown?

The correct answer is D.


34

Workshop Notes

Problem 29 Determine most nearly: a) The transformer turns ratio, a = N1/N2 b) The values of I1 and I2 in amps c) The primary-to-secondary impedance ratio d) The reflected input impedance in ohms

35

Workshop Notes

Problem 29/Contd. Solution: a) b) c) d)

1012120

2

1

VV

VVa

AAaII

AVRVI

L

12.0102.1

2.11012

21

22

2

2

1

2

22

1

11

100101000

102.1

12

100012.0

120

aZZ

AV

IVZ

AV

IVZ

1000)10()10( 22 xRaR LIN


36

Workshop Notes

Problem 30 A three-phase, 60Hz induction motor has a nameplate speed of 1800 rpm. This motor has how many poles? (A) 2.0 (B) 4.0 (C) 4.5 (D) 6.0 Solution: Synchronous speed is given by 120 f / p where f is frequency in Hertz and p is the number of poles. Thus, the correct answer is (B).

0.41800

)60()120(120

rpmHzx

nfp

S


37

Workshop Notes

Problem 31 What is the most correct statement that describes the phenomenon called aliasing in sampling theorem? (A) Aliasing is the presence of wanted components in the reconstructed signal. (B) Aliasing occurs when signal frequencies do not overlap if the sampling frequency is too low. (C) Aliasing is a phenomenon where the high frequency components of the sampled signal interfere with each other because of inadequate sampling. (D) All of the above. Solution: Aliasing leads to distortion in recovered signal. This is the reason why sampling frequency should be at least twice the bandwidth of the signal. The correct answer is (C).

38

Workshop Notes

Problem 32 A 12-bit analog-to-digital converter has a resolution of 1.75864 x 10 V/bit and the sum of the lowest voltage and highest voltage is 12.8V. The highest voltage is most nearly (A) 10 V (B) 14 V (C) 11 V (D) 12 V Solution; VH VL = 2v = 2 bits x (1.75864 x 10 V/bit ) = 7.2 V VH VL = 7.2 V VH + VL = 12.8 V (given in problem statement) Solving two equation with two unknowns, 2VH = 20 V VH = 10 V Thus, the correct answer is (A).


39

Workshop Notes

Problem 33 An engineer needs to design an analog-to-digital converter with a lowest voltage of 10 V and a highest voltage of 20 V, and a voltage resolution, v, equal to 0.000152588 V/bit. The number-bit of the analog-to-digital converter is most nearly (A) 10 bit (B) 8 bit (C) 16 bit (D) 12 bit Solution: Therefore, the converter should be designed to be a 16-bit analog-to-digital converter. The correct answer is (C).

1665536log

65536000152588.0

10202

2

n

VVVV

V

LHn


40

Workshop Notes

Problem 34 What is the voltage resolution of a 8-bit analog-to-digital converter if its highest voltage is 24 V and its lowest voltage is 12 V? (A) 6.2358 x 10 V/bit (B) 4.5875 x 10 V/bit (C) 5.3298 x 10 V/bit (D) 4.6875 x 10 V/bit Solution: The correct answer is (D).

V/bit 10 x 6875.4256

122

12242

2-

8

bitsV

VVVV

V

nLH

V

41

Workshop Notes

Problem 35 An analog-to-digital converter has produced 12 bits when its lowest voltage was 10V and its resolution 0.004488 V/bit. Find the discrete voltage value. (A) 10.235 V (B) 10.054 V (C) 10.077 V (D) 10.653 V Solution: Thus, the discrete voltage value is 10.054 V for a reading of 12 bits when the lowest voltage was 10V. The correct answer is (B).

VVVbitsbitVV

VNV LV

054.1010)12)(/004488.0(


42

Computers


43

Workshop Notes

Problem 1 What does CPU stand for in a computer system? (A) Certified Processor Unit (B) Complex Processing Unit (C) Central Processing Unit (D) Computer Program Unit Solution: CPU stands for Central Processing Unit. This is where all the computer's data processing is handled - all the data manipulation, calculations and formatting data for output. The correct answer is (C).

44

Workshop Notes

Problem 2 What type of computer memory stores a permanent set of start-up instructions, fixed at the time of the chips manufacture? (A) RAM (B) ROM (C) DRAM (D) HDD Solution: Your computers ROM is a chip on the motherboard that stores a permanent set of start-up instructions for your computer. Generally you can not alter the information in ROM; it is fixed at the time of manufacture. The correct answer is (B).

45

Workshop Notes

Problem 3 Which is larger a bit or a byte in computer terminology? (A) a bit is larger than a byte (B) a byte is larger than a bit (C) a byte is equal to a bit (D) None of the above. Solution: A bit is the smallest piece of information used by the computer. Derived from "binary digit". In computer language, a bit is either a one (1) or a zero (0). A byte is a piece of computer information made up of eight bits. Thus, a byte is larger than a bit. The correct answer is (B).

46

Workshop Notes

Problem 4 What is the clock speed of a computer processor? (A) The speed of the processor when the computer is fully charged (B) The speed of a computer processor in a moving vehicle (C) The speed of the rotating hard disk of a computer (D) The frequency (MHz) of a computers processor Solution: The execution of the instructions within the computer system is extremely fast and is measured in cycles of time and referred to as megahertz. For this reason the MHz of a computers processor is sometimes referred to as its clock speed. This pulsing is expressed as megahertz (MHz). The correct answer is (D).

47

Workshop Notes

Problem 5 What type of computer memory stores information in a temporary notepad fashion in a computer system? (A) RAM (B) ROM (C) HDD (D) CD - ROM Solution: RAM means Random Access Memory" (or sometimes "ready access memory"). It is like a temporary notepad where your computer sends information it has processed before writing it to disk, or where instructions from other input devices (keyboard, mouse floppy drive) are stored. The words "random access" indicate that memory locations in RAM are accessible in any order unlike sequential access of a data cassette tape, for example. The correct answer is (A).

48

Workshop Notes

Problem 6 What is the operating system in a computer? (A) A set of programs directly controlled by the computer operator. (B) A set of programs that run the system and make all the other programs work. (C) A set of programs in a computer that run when the computer is off. (D) A set of programs in a computer that only work at boot-up. Solution: Every computer needs a set of programs called the operating system to run the system and make all the other programs work. The word processor, database or spreadsheet programs can not operate unless the operating system is present. Programs written for one operating system will not work on a different operating system. Common operating systems include: Windows 7, Vista, Macintosh OSX and Linux. There are many versions aimed at different uses. The correct answer is (B).

49

Workshop Notes

Problem 7 A computer program contains the following segment:

50

Workshop Notes

Problem 8

51

Workshop Notes

Problem 9

INT(n) = m m n n A# 5 5

10.4 10

- 10.4 - 11

52

Workshop Notes

Problem 10 What would be the output of the following FORTRAN program? 10 DEF FNA (X,Y) = X*2 + X*3 X*Y 20 DATA 3,2,4 30 READ B(1), C, D 40 PRINT FNA (B(1), B(1)) 50 PRINT FNA (C/D, C*D) 60 END

B(1) = 3, C = 2, D = 4

Call FNA for (3, 3) Call FNA for (, 8)

F(x, y) = 2x + 3x xy

= 5x xy

FNA (3, 3) = 15 9 = 6

FNA (, 8) = 5/2 8/2 = - 3/2 = - 1.5

53

Workshop Notes

Problem 11

J = J + I Pass 0 1 2 3

J 0 1 5 34

I 1 2 3 I = 3

Go to 16

Exit

54

Workshop Notes

Problem 12

1.22443

432231.1

43

4105.11451.1 2

A

55

Workshop Notes

Problem 13

56

Workshop Notes

Problem 14

B C

7

8 B7*9 C7*9

57

Workshop Notes

Problem 15

A G 5 7

8

4 4 7 = 28

58

Workshop Notes

Problem 16 In a spreadsheet what is the easier way to write C5 + C6 + C7 + C8 + C9 + C10? (A) sum(C5:C10) (B) @C5..C10 (C) sum(B5:B10) (D) total(C5:C10) Solution: Answer is A sum(C5:C10) or Sum(C5:C10) or @sum(C5:C10) or Sum(C5:C10); it is not case sensitive.

59

Workshop Notes

Problem 17

= 64 = 519

J

60

Workshop Notes

Problem 18 In a spreadsheet, the content in cell A4 is set to 6. Then, A5 is set to A4 + $A$4. This formula is copied into cells A6 and A7. The number that appears in Cell 7 is most nearly:

6 = A4 = A4 + $A$4 = A5 + $A$4 = A6 + $A$4

A

4 6 6

5 6+6 12

6 12+6 18

7 18+6 24

$A$4 = 6

61

Ethics


62

Workshop Notes

Problem 1

63

Workshop Notes

Problem 2

64

Workshop Notes

Problem 3

65

Workshop Notes

Problem 4

66

Workshop Notes

Problem 5

67

Workshop Notes

Problem 6

68

Workshop Notes

Problem 7

69

Workshop Notes

Problem 8

70

Workshop Notes

Problem 9

71

Workshop Notes

Problem 10

72

Workshop Notes

Problem 11

73

Workshop Notes

Problem 12

74

Workshop Notes

Problem 13

75

Workshop Notes

Problem 14

76

Workshop Notes

Problem 15

77

Workshop Notes

Problem 16

78

Workshop Notes

Problem 17

79

Workshop Notes

Problem 17 (Contd.)

80

Workshop Notes

Problem 18

81

Workshop Notes

Problem 19

82

Workshop Notes

Problem 19 (Contd.)

83

Workshop Notes

Problem 20

84

Workshop Notes

Problem 21

85

Workshop Notes

Problem 22

86

Workshop Notes

Problem 23

87

Workshop Notes

Problem 24

To recuse = To disqualify oneself. To remove oneself from participation.

88

Workshop Notes

Problem 25

89

Workshop Notes

Problem 25 (Contd.) Solution: Answer is C. Giving few hours additional time is reasonable but week late is not fair to other bidders unless they were provided the same time in advance. Opening bids and letting estimator of the sixth company know is not acceptable. Choice C is the right way.

90

Workshop Notes

Problem 26

91

Workshop Notes

Problem 27

92

Workshop Notes

Problem 28

93

Workshop Notes

Problem 28 Solution: Answer is D Mike can not authorize technician to seal plans without the review of Luis who is responsible. City engineer is not the responsible engineer either. Only choice here is wait until Luis reviews and authorizes sealing of work.

Documents

Electricity CPUs Ethics Solutions