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ENB103-T1-S2-2007 - GUT III-I Examination Paper SEMESTER...

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Unformatted text preview: GUT III-I..- Examination Paper SEMESTER: SECOND SEMESTER EXAMINATIONS 2007 UNIT: ENBiOS ELECTRICAL ENGINEERING - THEORY 1 DURATION OF EXAMINATION: PERUSAL: 10 MINUTES WORKING: 2HOURS EXAMINATION MATERIAL SUPPLIED BY THE UNIVERSITY: EXAMINATION BOOKLETS MARK SENSE SHEET EXAMINATION MATERIAL SUPPLIED BY THE STUDENT: WRITING IMPLEMENTS 2B PENCILS ERASER CALCULATORS ~ ANY TYPE INSTRUCTIONS TO STUDENTS: Students are prohibited from having mobile phones or any other device capable of communicating information (either verbal or written) in their possession during the examination NOTES MAY BE MADE ONLY ON THE EXAMINATION PAPER DURING PERUSAL TIME §EQTIQN A - ALL TWENTY (20) QUESTIONS ARE TO BE ATTEMPTED ON THE MARK SENSE SHEET Sm - TWO (2) QUESTIONS ONLY ARE TO BE ATTEMPTED MARKS FOR EACH QUESTION ARE AS INDICATED Queensland University of Technology GUT GUT GUT GUT Gardens Point Kelvin Grove Carseldine Caboolture SECTION A Section A is compulsory. Answer all multiple choice questions. Select the most appropriate answer from the options given and indicate your selection on the mark-sense sheet provided. This section is worth 20 marks in total. All questions are of equal marks. QUESTION 1 Which of the following statements is true regarding the characteristics and use of a voltmeter to measure a DC voltage within a circuit? (a) A voltmeter has very high input resistance and is connected in series with a circuit element to make a voltage measurement (b) A voltmeter has very low input resistance and is connected in series with a circuit element to make a voltage measurement (0) A voltmeter has very high input resistance and is connected across a circuit element to make a voitage measurement ((1) A voltmeter has very low input resistance and is connected across a circuit element to make a voltage measurement QUESTION 2 Which of the following statements is true regarding the characteristics and use of an ammeter to measure a DC current within a circuit? (a) An ammeter has very high input resistance and is connected in series with a circuit element to make a current measurement (b) An ammeter has very low input resistance and is connected in series with a circuit element to make a current measurement (c) An ammeter has very high input resistance and is connected across a circuit element to make a current measurement ((1) An ammeter has very low input resistance and is connected across a circuit element to make a current measurement QUESTION 3 With reference to the circuit below, what is the equivalent resistance between A-B? (a) 6.09 Q. (b) 8.41 o. (c) 10.0 o. (d) 53.0 o. 5 n J——l—'"‘u"\fir"\lirfi“'—F—’—O A 2%? 12 r2 .5: 4 r2 2;} 20 o l___l—m wal‘ig'nvn‘ll'p'flsji-—--—L~—O B 12 o. ENB 1 03'1“} .072 contl. .. QUESTION 4 In the network shown in below, calculate the current in the 15 ohm resistor. (a) 0.25 A (b) 0.73 A (c) 0.132 A (d) 0.545 A .\ . ‘u‘. ,——[——— WA 7—1 '3- 3:. 10 ohms /+\\ «3:: 5 0111113 "'55: 15 ohms k .1 10 Volts 3/ QUESTION 5 Two resistors are connected in series. Select the one true statement. (a) They both must have the same resistance value. (b) The voltage across each must be the same. (c) They must have different resistance values. ((1) There is only one path for the current through both resistances. QUESTION 6 The output voltage of an ideal constant current source of magnitude one amp will be:- (a) One volt. (b) Zero volts. (c) Dependant on the remainder of the circuit. ((1) Independent of the remainder of the circuit. QUESTION 7 Select the one false statement. (a) Resistance in a circuit causes a voltage drop. (b) Resistance is the reciprocal of conductance. (0) Resistance of a short circuit is infinity ohms. ((1) Resistance is the constant that relates current to voltage. QUESTION 8 If a battery supplies 5 amps at a voltage of 12 volts, how much energy is delivered in 1 minute? (a) 5/60 A-h. (b) 60 Watts. (0) 2880 Joules. (cl) 3600 Joules. ENB103T1.072 cont/. .. QUESTION 9 A sinusoidal waveform has an angular frequency of 1000 rad/s. What is its frequency in Hertz? (a) 50 Hz (b) 159 Hz (0) 1 kHz (d) 6283 Hz QUESTION 10 A circuit has six capacitors in parallel, each with a value of 10 nF. What is the total combined capacitance of the circuit in 11F? (a) 0.06 11F (b) 60 pF (c) 1.7 ”F (d) 0.0017 111: QUESTION 11 A circuit has two inductors in parallel, each with a value of 10 mH. What is the total combined inductance of the circuit in mH. (a) 0.01 mH (b) 5 mH (c) 20 mH (d) 100 mH QUESTION 12 A sinusoidal signal has a peak to peak voltage of 100V. What is the RMS value of this signal? (a) 0 v (b) 35.4 V (c) 50.0 v (d) 70.7 V QUESTION 13 A resistor and capacitor combination has an overall impedance of Z = 50 a leO Q. What is the impedance phasor? (a) 11184—2660 o (b) 11184266" 9 (c) 411.23.463.40 Q (d) 11 13.4—63.4" 9 ENB103T1.072 contf... 4 QUESTION 14 Consider the following RLC circuit with C = 10 MP and L = 5 mH. Atwhat frequency (in Hz) does the circuit have a purely resistive impedance (ie. the impedance has a phase of 0°). C L ....._:.-..+ PT“‘WW (a) 10 Hz (b) 711.8 Hz (0) 4472 Hz (d) The circuit cannot not have a phase of 00 because C does not equal L. QUESTION 15 The complex power equation: S = Sl + 82 + + SN for N number of loads in a circuit is applicable to: (a) any ways that the loads are connected. (b) only series connected loads. (c) only parallel connected loads. ((1) none of the above. QUESTION 16 The Thevenin impedance of a network seen from the load terminals is 80 + jSS Ohms. For maximum power transfer, the load impedance must be: (a) ~80 +j55 Ohms (b) 80 —j55 Ohms (c) -80 — j55 Ohms (d) 80 +j55 Ohms QUESTION 17 If the load impedance is 20 — j20 Ohms, the power factor is: (a) -450 (b) 0.7071 (c) 0 (d) 1 QUESTION 18 In a power triangle, the real power is 500 W and the angle it makes with the apparent power is +600, what is the reactive power: (a) 1000 VAR leading (b) 1000 VAR lagging (c) 866 VAR lagging (d) 866 VAR. leading ENB103TLO72 cont/... QUESTION 19 What is the phase sequence of a three phase motor for which VAN = 220 volts with an angle —100° and VBN = 220 volts with an angle 140°. (a) bac (b) abd (c) cab ((1) none of the above. QUESTION 20 In a delta connected load, the line current and phase current are: (a) Equal. (b) Not equal. (0) equal in magnitude and 300 apart. (d) none of the above. ENB103T1.072 cont/... 6 SECTION B Answer only two of the questions in this section in the examination booklet provided. Show full working. Each question is worth 20 marks giving a total of 40 marks for this section. QUESTION 21 Consider the following circuit and answer the following questions. 29 19 1 2V 2V 3!) (21) Find the current flowing in the two meshes in the above circuit. (14 marks) (1)) Find the voltage across the 39 resistor. (6 marks) (20 Marks Total) QUESTION 22 Consider the circuit below where is(t) = Ssin(1000t) amps. 10 £2 110‘) 1'30) Perform the following: (a) Sketch the phasor diagram clearly showing the phasors for 1'30), X3 and XL. You must clearly label the magnitude and angle of each phasor. (6 marks) (b) Using mesh analysis, calculate the currents 1' 1(1‘) and i2(t) (in amps) expressing your answers in the form i(t) I Asin(a)t+ a). ( 14 marks) (20 Marks Total) ENB l 03T'l .072 cont/. .. QUESTION 23 Find: (a) The total number of WATTS, VAR and VA, and the power factor, pf, for the network below. (8 marks) (b) Sketch the Power Triangle (6 marks) (c) Find the energy dissipated by the resistor over one full cycle of the input voltage if the frequency of the input is 60Hz. (6 marks) E=1Ifl0 I} (20 Marks Total) END OF PAPER ENB103T1.072 ...
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