Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

1

Faculty of Information

Engineering & Technology (IET) Electronics Engineering Dept.

Electric Circuits II: ELCT 401 Final Exam (May 2013)

Course Instructor: Prof. Yasser G. Hegazy

Instructions:

1. Answer all questions.

2. The exam consists of 5 questions + 1 Bonus question in 13 pages.

3. A formula sheet is attached at end of this booklet.

4. The exam allowed time is 3 hours.

5. Electronic calculators are allowed.

6. Clearly show all steps used in your solutions.

7. This is a closed book exam.

Please, do not write anything on this page

Total Mark Bonus 5 4 3 2 1 Question

Mark

48 2.0 10 01 10 8 10 Out of

Bar Code

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

2

Question # 1 [ 10 Marks ]

In the circuit shown in Fig. 1; the total reactive power of the circuit is 2500 VAR (inductive)

a) Find the active power of each branch and the total active power. [ 6 Marks ]

b) Calculate the total apparent power and the circuit power factor. [ 4 Marks ]

Fig. 1

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

3

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

4

Question # 2

In the circuit shown in Fig.2,

a) Find the resonant frequency . [ 4 Marks ]

b) Find the Bandwidth. . [ 4 Marks ]

Fig.2

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

5

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

6

Question # 3 [ 10 Marls ]

In the circuit shown in Fig. 3, assume zero initial conditions,

a) Use “S” domain analysis; Find an expression for the transfer function H(S) = Vo(S) / VS(S) [6 Marks]

b) Calculate Vo(t) when Vs(t) = 10 cos (10 t+300), [4 Marks]

Fig. 3

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

7

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

8

Question # 4 [10 Marks]

A filter circuit is shown in Fig. 4:

a) Write an expression for the filter transfer function Vo()/VS(). [4 Marks]

b) Determine the filter type. [2 Marks]

c) Based on the filter type, calculate the filter cut off frequency or frequencies. [4 Marks]

Fig. 4

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

9

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

11

Question # 5 [10 Marks]

For the circuit shown in Fig. 5, find Ib and Z if Vg = 25 cos t V and Ia = j 5 A

Fig. 5

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

11

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

12

Bonus Question

A circuit with impedance Z =10 < 600 has the power factor improved by a capacitive reactance of 20 .

What is the percentage reduction in the circuit current? What is the new power factor?

Final Exam Electric Circuits II (ELCT401) Time allowed : 3 hours

13

Formula Sheet

1. Power Calculations

zivS

Prpowerfacto

jQPivrms

Irms

Vjivrms

Irms

VS

cos)cos(

)sin()cos(

2. Resonance

Connection Resonance

Frequency Quality Factor Band Width

Half Power

Points

Series

Parallel

3. Laplace Transform