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(ELEC102)test2_pasti.pdf
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(7)

(7)

1

(a)



Text Box: Hence EC and EL must be continuous with time (unchanged after switching)

Text Box: Another short proof



(17)

2k.

v(t)

(4)

20m

2k.

1mH

v(t)

i(t)

(3)

(3)

(3)

(4)

2k.

v(t)

i(t)

i(t)

(i)


Text Box: The switch has been closed for a long time. At t = 0 second, the switch is opened. (i) If X = 1mH, find i(0) , i

1

(7)

2k.

30V

(4)

2k.

1mF

30V

i(t)

(3)

(ii)

v(t)

i(t)


Text Box: (ii) If X = 1mF, find v(0) , i(0) for t .d 0 . Given that i(t) = i(.V) +[i(0) - i(.V)] exp(-t/..) . (7)




Text Box: 6k..


Text Box: t .d 0

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2

(3)

(2)

(6)



Text Box: (24)


Text Box: (a)
Text Box: (b)




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(4)

(2)



Text Box: (c)


Text Box: i(t) leads v(t)
Text Box: If i(t) = 5cos(1kt + 30o)A , v(t) = 20cos(1kt - 30o)V , and Z is R in series with X. Find Z in .. . Fin


(17)

3


Text Box: (a) If , find . Draw also the
Text Box: (5)
Text Box: (4)

3

(6)

(b)





Text Box: (b) If v(t) = Vm cos ..t, express the impedance Z in terms of R, L , C and .. . (6)


(b)

(21)

4

(a)

(3)

(c)

or

(4)



(15)

5

(a)

(9)

(6)


Text Box: Add load D to make PF = 0.9 lagging (capacitance C)
Text Box: If a load D is connected in parallel to load B to make the total power factor = 0.9 lagging, find the element and val





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(9)

(4)

(b)

5

Text Box: For load A, the apparent power S is 2200VA, and the reactive power Q is Find the average p





6

(21)

(5)

(6)

(6)

(4)



Text Box: (b) The power factor of Load C is 1, find I in Arms . If load B is R in series with X. Find R in .. .
Text Box: Load A

Text Box: 220.0o Vrms50Hz
Text Box: Electric fees is related to P onlyP is unchanged hence fees will not be reduced
Text Box: (a)
Text Box: (a) Will electricity fee be reduced if the power factor is improved to 1? Why? (21)


Text Box: (b)


7

(5)

(6)

(7)

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(5)







Text Box: (a) If Va = 1V, find Vb , Vc and Ia . (b) If Va = 10V, find Vc . Given X = 8k.. , R1 = 1k.. , R = 2k.

Text Box: If Va is changed to 10V, Vc = 15V (op amp saturated)
Text Box: (a)
Text Box: (b)


8

-3j

j

(8)

(6)

(14)

-3j

j




Text Box: Find Va . The voltage dependent current source is in ampere and equal to 0.5Va. (14)







9

(25)

(3)

(a)

(b)

(d)

(c)

0.7Vo







Text Box: Change R to 2R




10

(13)

(4)

(4)

(5)



Text Box: Z = R = 0.05..

Text Box: The series LCR circuit is in resonance . R is 0.05? and Find Z, resonant frequency fo in Hz, and v(t).






(16)

+
VO
-

(7)

(b)

8