Family Name ……………………………….. Given Name ………………………………… Student No. …………………………………. Signature ……………………………………
THE UNIVERSITY OF NEW SOUTH WALES School of Electrical Engineering & Telecommunications MID-SESSION EXAMINATION
S1 2015
ELEC1112
Electrical Circuits
TIME ALLOWED:
TOTAL MARKS:
TOTAL NUMBER OF QUESTIONS:
55 minutes 40
5
THIS EXAM CONTRIBUTES 20%TO THE TOTAL COURSE ASSESSMENT
Reading Time: 5 minutes.
This paper contains 4 pages.
Candidates must ATTEMPT ALL questions.
Answer all questions in the answer booklet provided.
Marks for each question are indicated beside the question.
This paper MAY be retained by the candidate.
Print your name, student ID and 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.
QUESTION 1 [12 marks]
(i) (4 marks) For the circuit in Figure 1 below, calculate the equivalent resistance of the network as seen from the terminals shown.
Figure 1.
(ii) (8 marks) For the circuit below in Figure 2,
a) Determine the voltage and current .
b) Determine the power absorbed or supplied by the resistors and the current sources. For each element, you should specify whether the power is absorbed or supplied.
1
+
1A 1 V 3A
–
Figure 2.
I
2A 5
Page 2
QUESTION 2 [6 marks]
For the circuit shown below in Figure 3, use mesh analysis to write down enough equations to be able to solve for the mesh currents labelled , , and . (Note: You should NOT solve them)
Figure 3.
QUESTION 3 [8 marks]
For the circuit below in Figure 4, and showing sketches in your working, use the superposition principle to determine the current that would flow in the 12 resistor.
20
60
10
Figure 4.
20V
A
12 B
6A
Page 3
QUESTION 4 [6 marks]
For the circuit below in Figure 5, find the Thévenin equivalent circuit with respect to the terminals A,B.
40
A 60 5A 12
B
Figure 5.
For the circuit below in Figure 6, the switch has been open for a long time before closing at time t = 0.
(i) (4marks)Calculatethecapacitorvoltageimmediatelyaftertheswitchcloses,i.e. 0, and as → , i.e. lim .
for t > 0. Explain how you arrived at this expression.
+ –
Figure 6.
END OF PAPER
800V
QUESTION 5 [8 marks]
→
(ii) (4marks)Giveanexpressionforthecapacitorvoltage(i.e.asafunctionoftime)
Page 4