EEE121 April 2011

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CONFIDENTIAL EE/APR2011/EEE121

UNIVERSITI TEKNOLOGI MARAFINAL EXAMINATION

COURSECOURSE CODEEXAMINATIONTIME

ELECTRIC CIRCUIT IEEE121APRIL 20113 HOURS

INSTRUCTIONS TO CANDIDATES1 . This question paper consists of five (5) questions.

Answer ALL questions in the Answer Booklet. Start each answer on a new page..3.

4.

Do not bring any material into the examination room unless permission is given by theinvigilator.Please check to make sure that this examination pack consists of:

i) the Ques tion Paper.ii) A on e-p ag e Appendix (Magnetisation Curve)iii) an Ans wer Booklet - provided by the Faculty.

DO NOT TURNT ISPAGEUNTILYOU ARE TOLD TO DO SOThis examination paper consists of1 printed pages Hak Cipta Universiti Teknologi MARA C O N FI D EN TI AL

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CONFIDENTIAL 2 EE/APR 2011/EEE121

QUESTION 1

a) Define what an active element is and giveONEexample of that eleme nt. (1 m arks)b) i) Sketch the waveform a nd describe the differences of the two comm on types ofcurrent.

(2 marks)ii) A 2.2 kW hair dryer produces a current of 10 A. Estimate the voltage acrossthe appliance.

(1 marks)c) Encik Saiful has two ho uses. If the first house used 680 kW h and the other house used320 kWh for a month, calculate his total monthly electricity bill.

TNB charges customers as follows;

Rate 1: Usage of 0 - 400 kW h per monthFirst 200 kWh 21 .8 cents / kWhNext 200 kWh (201 - 400 kWh) 33.4 cents / kWhMinimum monthly charge RM 3.00

Rate 2: Usage of more than 400 kWh per monthFirst 500 kWh 28.6 cents / kWhNext 100 kWh (501 - 600 kWh) 37.8 cents / kWhNext 100 kWh (601 - 700 kWh) 38.7 cents / kWhMinimum monthly charge RM 3.00

(6 marks)

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CONFIDENTIAL 3 EE/APR2011/EEE121

d) For the circuit show n in Figure Q1d.Determine the current l0, using successive SourceTransformation.

2 0 Q

5 Q-A/vV5 A

10Q-AAAr10V

20 Qr -WV-t20 Q

10 V|

8 Q

20 V

Figure Q1d (10 m arks)

QUESTION 2

a) Define the Kirchoff's Law, and briefly explain why the word 'algebraic sum' is used.(3 marks)b) For the circuit show n inFigure Q2b,i) write down the K irchoff's Voltage Law (KVL) equation for each loop,

ii) get the voltage V3, V 4 , and V 5.

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RiAAAr

15V

R2A A A r+ 2 5 V - - 1 0 V +

2 0 v QR3-A/Wv, -

V 4 ^ R4 v 5 < R 5

Figure Q2b (4 m arks)c) Apply Current Divider Rule (CDR) to find lsfor the circuit shown inFigure Q2c.

Figure Q2c (3 marks)


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d) List down the formula for the following terms inTable Q2d.Table Q2d

TermsFlux density

Relative permeabilityMagnetic flux

Magnetomotif force

Formula

(2 marks)e) The core of the magnetic circuit shown in Figure Q2e is made of cast steel. The cross

sectional area throughout the core is 0.5 x 1 0 4m2and the length of the air gap is2 m m, number of turns, N is 200 and the permeability of free space is Kx 10 7H/m. W ith the m agnetization curve of the magnetic m aterials as given inAPPENDIX 1.(Neglecting the magn etic leakage and fringing effect).i) Draw the magnetic equivalent circuit.ii) Determine the current I, required to establish a magnetic flux of 0.1 5 x 1 0 W b in the

air gap.

TTT

550 mm

j i k .

FigureQ2e

Hak Cipta Universiti Teknologi M ARA

IS

turns cc

a b

f

Air gap--j 2 mm^

ri// /

9|IIe550 mm

/

c

5 50 mmd

^ ^

^ ^

(8 marks)CONFIDENTIAL

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QUESTION 3

a) For the circuit show n inFigure Q3a,by using Y to A Transformation T echnique, obtain:i) the equivalent resistance at terminal a - b .ii) the voltage acro ss 30 Q resistor, Vx.

40 V

30 QAAAr a+ Vx100ftV W

100 f t100 ft-A/W

100 ft100ft-A/W-

100ft- V W -1 0 0 f t

1 0 0 f t100ftAA/V-

1 0 0 f t

>100ft

Figure Q3a(10 marks)

b) Find the Theve nin equ ivalent circuit at termina ls a-b for the circuit of Figure Q3b andhence determine the possible maximum power delivered to the load R.1ft-AA/V

v(

2ft A / W

+1ft< v 0 > 0 . 3 V 0

Figure Q3b (10 marks)

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QUESTION 4

a) State whether the statemen ts below areTRUE or FALSE :i) a capacitor is an elemen t designed to store energy in its magneticfield,ii) an inductor is an element designed to store energy in its electric field.

(2 marks)

b) Four induc tors, L1 = 4 mH, L2 = 12 mH, L3 = 8 mH, and L4 = 5 mH are connected inparallel across a 4 A source. Determine:i) the total equivalent inductance.ii) the current acro ss inductor L2.i ii) the total energy stored in the equivalent inductance.

(4 m arks)c) The voltage response across a 5 uF capacitor is shown in Figure Q4c Determine thecurrent for each tim e interval and sketch resultant capa citor current response.

vc(V)i

100

-10

Figure Q4c(4 m arks)

*- t(ms)

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CONFIDENTIAL EE/APR2011/EEE121

d) By applying Mesh Analysis Technique, calculate lxand V0 for the circuit shown inFigure Q4d

120V40 nVW

i on-AAAr

100V

20 n-AA/V-

;5on

Figure Q4dA - Y 2,^ )(l)-3 ::L ^ i 1 >80n

(10 marks)

QUESTION 5

a) With the aid of suitable diagra m, explain the procedure to get the voltage relationshipwhen there is voltage source between two non-reference nodes. (3 marks)

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b) For the circuit show n in Figure Q5b, label the non-reference nodes and hence find thenode voltages.

o 10Q

c) State the Supe rposition Theo rem.(7 marks)

(2 marks)


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d) Calcu late the curren t I, show n inFigure Q5dby using Superposition Theorem.

2 0 v Q2Q h r- V V V 1

c c

R,R 2+R2R3 +R3R1

END OF QUESTION PAPER


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CONFIDENTIAL APPENDIX 1 EE//APR2011/EEE121

Magnetisation Curve,

Z1SUit steel

Cast steel

Cas ttrim

100 200 300 400 500 600 700

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EEE121 April 2011

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