Family Name Other Names Global ID Date
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Diplomas
Electrical and Telecommunications Engineering
EE1111
Question
Possible Marks
Actual Marks
1
30
2
30
3
40
Total
100
Mid-Semester Exam Reading time: 10 minutes Working time: 80 minutes
Term: T2 2020
UNSW Diplomas
UNSW Global Pty Limited
UNSW Sydney NSW 2052 Australia
Copyright 2020
All rights reserved. Except under the conditions described in the Copyright Act 1968 of Australia and subsequent amendments, this publication may not be reproduced, in part or whole, without the permission of the copyright owner.
Directions to Candidates
This paper contains 7 pages.
Candidates must ATTEMPT ALL questions.
Answer each question in a separate answer booklet.
Marks for each question are indicated beside the question.
This paper MAY NOT be retained by the candidate.
Print the question number on the front page of each answer book. Authorised examination materials:
Candidates should use their own UNSW-approved electronic calculators.
This is a closed book examination.
Assumptions made in answering the questions should be stated explicitly.
All answers must be written in ink. Except where they are expressly required, pencils may only be used for drawing, sketching or graphical work.
For the numerical solutions, you can use either fraction form or floating-point form (maximum 2 digits after decimal point is enough)
QUESTION 1 [30 marks]
(i) [10 marks] For the circuit shown in Figure 1:
a. (8marks)Calculatetheequivalentresistance.
b. (2 marks) If the resistance of each individual resistor is R=11Ω, find current io.
R
io R R
RRRR
Req
Figure 1 (ii) [20 marks] For the circuit shown in Figure 2,
a. (5 marks) Apply mesh analysis and show that mesh equations are given as below:
100 V
10𝑖2 − 20𝑖1 = −400 { −10𝑖1 + 20𝑖2 = 0
𝑖3 = −10 𝐴
b. (5 marks) Given the values of mesh currents as i1 = 80 A, i2 = 40
A and i3 = -10 A and i3 = -10
A, find 𝑉 . 0
33
c. (10 marks) Given the values of mesh currents as i1 = 80 A, i2 = 40
A, calculate the power supplied by each source.
i1 i2
i3
33
Figure 2
QUESTION 2 [30 marks]
(i) [20 marks] In the circuit of Figure 3, the switch has been in the open position for a long time before closing at time 𝑡 = 0. Find the current through the 1 Ω resistor at t=0+.
t=0
2
5V io
1F
22
Figure 3
1
2
(ii) [10 marks] In the circuit of Figure 4, Apply nodal analysis to find current ix (Use the given current directions in the circuit in deriving your nodal equations).
ix
+-5ix 3 6A
Figure 4
5 54A4
50 V
QUESTION 3 [40 marks]
(i)
[20 marks] Find the Thevenin equivalent of the circuit given in Figure 5.
0.25 vx
4
6
+
a
b
8V 3A vx 4
–
Figure 5
(ii)
[20 marks] In the circuit of Figure 6, the switch has been in the close position for a long time before opening at time 𝑡 = 0:
a. (2 marks) Find the capacitor voltage 𝑣𝑐(0) for 𝑡 < 0.
b. (15 marks) Give an expression for the capacitor voltage 𝑣𝑐(𝑡) (i.e., as a
function of time) for 𝑡 > 0.
c. (3marks)Giveanexpressionforthe6-Ωresistorcurrent𝑖6Ω(𝑡)(i.e.,asa
function of time) for 𝑡 > 0.
5 6
+ 12 201FVc
t=0
2A
20 V
Figure 6
“End of the Paper”
–
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