# CS计算机代考程序代写 Family Name ……………………………….. Given Name ………………………………… Student No. …………………………………. Signature …………………………………….

Family Name ……………………………….. Given Name ………………………………… Student No. …………………………………. Signature …………………………………….

THE UNIVERSITY OF NEW SOUTH WALES School of Electrical Engineering & Telecommunications MID-SESSION EXAMINATION

SUMMER 2016 – 2017

ELEC1111

Electric Circuits

TIME ALLOWED:

TOTAL MARKS:

TOTAL NUMBER OF QUESTIONS:

60 minutes 40

5

THIS EXAM CONTRIBUTES 15% 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 NOT 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 [6 marks]

(i) (4 marks) For the circuit in Figure 1 below, calculate the equivalent resistance of the network as seen from the terminals a – b.

16 Ω 16 Ω

8Ω 8Ω

a

8Ω

4Ω

Figure 1.

(ii) (2 marks) Calculate the ratio of power consumed in resistors R1 (P1) and R2 (P2) as

P2/P1

QUESTION 2 [8 marks]

For the circuit shown below in Figure 2,

(i) (4marks)Calculatethecurrenti2

(ii) (2 marks) Calculate the power supplied/absorbed by the dependent current source. (iii)(2 marks) Calculate the power supplied/absorbed by the independent voltage source.

8Ω

4Ω R2 b

R1

2Ω 2Ω

10 V

20 Ω

+ ‐

5 Ω

i1i2 i3 10 Ω 0.5i1 20 Ω

Figure 2.

1 A

Page 2

QUESTION 3 [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 using the notations given in the Figure. (Note: You should NOT solve them)

2Vx

Mesh 3

1Ω

1Ω

1Ω

2A

Mesh + ‐‐

2Ω

Figure 3.

+ Mesh

3V 11Ω 2Vx1Ω

QUESTION 4 [10 marks]

For the circuit below in Figure 4, showing all working,

(i) (4 marks) Find the Thévenin equivalent circuit with respect to the terminals a-b.

(ii) (1 mark) Calculate the current through resistor R when R= 3 kΩ.

(iii) (5 marks) Calculate the current through resistor R when R= 3 kΩ using superposition

theory.

4 kΩ

12 V

3 kΩ

+ ‐

a

R b

Figure 4.

2 mA

2 kΩ

Page 3

+‐

QUESTION 5 [10 marks]

For the circuit below in Figure 5, the switch has been in the open position for a long time before closing at time t = 0.

(i) (6marks)Giveanexpressionforthecapacitorvoltagevc(t)(i.e.asafunctionoftime) for t > 0.

(ii) (2 marks) Give an expression for the capacitor current ic(t) (i.e. as a function of time) for t > 0.

(iii)(2 marks) Give an expression for the current of the 40 Ω resistor iR40(t) (i.e. as a function of time) for t > 0.

10 Ω

40 Ω

1 m F

Figure 5.

END OF PAPER

50 Ω

t = 0

10 V

+‐

+‐ 3 5 V

Page 4