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ECE 201 – Exam 2 (Fall 2013)

October 15, 2013

Section 2: Pekarek (3:30 pm)

Section 4: Jiao (1:30 pm)

Section 5: Lin (11:30 am)

Instructions

1. DO NOT START UNTIL TOLD TO DO SO.

2. Write your name, division, professor, and student ID# (PUID) on both your scantron sheet and your work-out sheet.

3. This is a CLOSED BOOKS and CLOSED NOTES exam.

4. This exam has two parts:

Part A contains 9 multiple-choice questions, each worth 10 points except Problem 5 (which

is worth 5 points). There is only one correct answer to each question. Only answers marked

on your scantron sheet will be graded. Partial credits will NOT to be given to Part A.

Part B contains 1 work-out problem worth 15 points. Only answers written on the work-out

sheet will be graded. Clearly show intermediate steps in order to receive partial credits.

5. Calculators are allowed (but not necessary). Please clear any formulas, text, or other information from your calculator memory prior to the exam.

6. If extra scratch paper is needed, use back of test pages. If extra work-out sheet is needed, ask the instructor.

7. Cheating will not be tolerated. Cheating in this exam will result in an F in the course.

8. As described in the course syllabus, we must certify that every student who receives a passing grade in this course has satisfied each of the course outcomes. On this exam, you

have the opportunity to satisfy the following outcomes. (See the course syllabus for a

complete description of each outcome.) On the chart below, we list the criteria we use for

determining whether you have satisfied these course outcomes. You only need to satisfy the

outcomes once during the course, so any outcomes that you satisfied previously will remain

satisfied, independent of your performance on this exam.

Course

Outcome

Exam

Questions

Minimum correct answers

required to satisfy the course

outcome

i 1-3,10 2

ii 4-10 3

Formulas that you may need: ot t /

ox(t) x( ) x(t ) x( ) e , = L/R, = RC

Elapsed time: o0x(t ) x( )

t t logx(t) x( )

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PART A: 9 Multi-Choice Questions

IMPORTANT: Only answers marked on

your scantron sheet will be graded!!!

One correct answer for each question.

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1. Find the Thevenin equivalent circuit when looking into terminals a and b of the circuit

below:

(1) A 6 V source in series with a 2 Ohm resistor (2) A 6 V source in series with a 1 Ohm resistor (3) An 8 V source in series with a 1 Ohm resistor (4) A 6 V source in series with a 2/3 Ohm resistor (5) A 40 V source in parallel with a 2/3 Ohm resistor (6) An 8 V source in series with a 2 Ohm resistor (7) A 6 V source in series with a 4/3 Ohm resistor (8) None of the above

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2. Suppose that you take the following measurements on the 2-terminal linear circuit in

the box below. When = , you measure = 25 V. When Ω, you measure = 5 V. Now, if Ω, find the value of .

(1) 1.25 V (2) 2.5 V (3) 10 V (4) 25/9 V

(5) 5 V (6) 3/4 V (7) 0 V (8) none of the above

2-Port

Linear CircuitLRLV

Li

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3. A 2-Port linear circuit, such as that shown below, has a measured open-circuit voltage

of 10 V. The measured short-circuit current is 2.5 A. The maximum power that can be

delivered to a load resistance is

(1) 50 W (2) 25 W (3) 22.5 W (4) 100 W

(5) 35 W (6) 25/8 W (7) 30 W (8) none of the above

2-Port

Linear CircuitLRLV

Li

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4. The current iC(t) flowing through a capacitor of capacitance C = 1 F is shown in the

figure below. The current before t = 0 is 0. Which of the following figures represents the

voltage VC(t)?

1)

2)

3)

4)

5)

6)

iC(t) (A)

t (s)1 2 3 4 50

1

−1

C=1 F

iC(t)

VC(t)

+

−

VC(t) (V)

t (s)1 2 3 4 50

1

−1

VC(t) (V)

t (s)1 2 3 4 50

1

−1

VC(t) (V)

t (s)1 2 3 4 50

1

−1

VC(t) (V)

t (s)1 2 3 4 50

1

−1

VC(t) (V)

t (s)1 2 3 4 50

1

−1

VC(t) (V)

t (s)1 2 3 4 50

2

−1

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5. Find the equivalent inductance Leq of the following circuit.

1) 12 H 2) 7 H 3) 19 H

4) 14 H 5) 11.5 H 6) None of the above.

6. For the circuit shown below, is(t) = 2 sin(2t) A, and VL(t) is the voltage drop from node A to

node B. Find ic(t).

1) −96sin (2t) A 2) −24sin (2t) A 3) −12sin (2t) A

4) 48cos(2t) A 5) 24sin(2t) A 6) 12cos(2t) A

Leq

3 H

6 H

5 H

5 H

+

−iS(t)=

2sin(2t) A

+

−

A

3 F

2 H

VL(t)

6 F−

1 H

iC(t)

B

2VL(t)

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7. Suppose that right before t=1s, the voltage of the capacitor is Vc(1-)=5V. Find the voltage

VC(t) (in V) as a function of time for t ≥ 1:

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

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8. Suppose that at t=0s, the current through the inductor is IL(0)=1A. Find IL(t) (in A) as a

function of time for t ≥ 0:

(1) 3-2e-t (2) 3-2 e-2t/9

(3) 0.5+0.5e-t (4) 0.5+0.5e-2t/9

(5) 1+2e-t (6) 1+2e-2t/9

(7) 1-0.5e-t (8) 1-0.5e-2t/9

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9. Find the initial value at t=0+, the final value at t= , and the time-constant for the voltage Vc

across the 200mF capacitor (for t ≥ 0).

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

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PART B: 1 Work-Out Question

IMPORTANT: Only answers written on your workout

sheet will be graded!!!

Clearly show intermediate steps in order to receive

partial credits.

Make sure you write your name, division, professor,

PUID on the work-out sheet.

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Workout Sheet for Part B

Name: _______________________ PUID:______________ Division: ____ Professor: ______

1. In the circuit shown, the switch is closed at t=0s. Let IL denote the current through the

inductor.

(1) Find the value of IL(0+) immediately after the switch is closed at t=0s.

(2) Find the Thevenin equivalent for the 2-terminal network seen from the inductor after the

switch is closed at t=0s.

(3) Find the value of IL(t) at t=1s. (Hint: You may want to use the Thevenin equivalent that you

have obtained in Step 2 to simplify the circuit.)