This is a closed book exam, but you are allowed a calculator and a single 8.5 x 11 sheet of notes.

You must SHOW YOUR WORK to receive credit on any problem.

Write clearly: work which is not legible WILL NOT COUNT towards your grade.

Numeric answers MUST HAVE UNITS to be correct (i.e., 3, 2A, 4mV)

Always good exam policy:

(1) READ THROUGH THE ENTIRE EXAM BEFORE BEGINNING

(2) WORK ON THE SIMPLER PROBLEMS FIRST

(3) TRY TO ANSWER ALL PROBLEMS

University of California San Diego Department of Electrical and Computer Engineering

ECE 35 Winter 2010 Practice Final Exam A

Signature _____________________________________

Name (Last, First) _____________________________

Student ID Number _____________________________

Grade

1 _________ / 20

2 _________ / 20

3 _________ / 20

4 _________ / 20

5 _________ / 20

6 _________ / 20

7 _________ / 20

8 _________ / 20

9 _________ / 20

__________________

_________ / 180

Problem 1 (20 pts): For each case, calculate the value which will be displayed by a real meter and say (Y/N) whether the value is accurate, defined as within 5% of the value which would be shown by an ideal meter.

Real voltage meter: Vmeasured = _____________ Accurate? ____ (with 1M internal resistance)

Real voltage meter: Vmeasured = _____________ Accurate? ____ (with 1M internal resistance)

1M 6V voltage meter

+

-

Real current meter: Imeaasured = _____________ Accurate? ____ (with 0.01 internal resistance)

1 A current meter

+

-

0.01

1M 6V voltage meter

+

-

1M

Real current meter: Imeasured = _____________ Accurate? ____ (with 0.01 internal resistance)

current meter

+

-

0.01

6V

Problem 2 (20 pts): Find the Thevenin and Norton equivalent values for the circuit below

4i

R1 IS i

a

b

R2

2A: Vth = _________________

2B: In = _________________

2C: Rth = _________________

Problem 3 (20 pts):

For the opamp circuit at right, calculate the following:

3B (5 pts): vin = _______

3C (5 pts): vout = _______

3D (5 pts): iL = _______

3A (5 pts):You used a circuit similar to the one at right in one of your labs.

Briefly state what it was used to do:

+

-

Vin

RLOAD

Vout 2.5V

+

-

5V

C

R

vin 5V

+

-

-

+ 20 k

10 k

0.1 mA vout +

-

iL

Problem 4 (20 pts): In the circuit below, the switch was open for a long time then closed at ts = 5 seconds.

4A: What is the voltage VC just before switching ( t < ts )? VC ( t < ts ) = ______________ 4B: What is the voltage VC long after switching ( t >> ts )? VC ( t >> ts ) = ______________ 4C: What is the time constant for the circuit after switching? = ______________ 4D: What is the equation for voltage Vc after switching? VC( t > ts ) = ____________________________

4E: Sketch the voltage from t = 0 on the graph below; be sure to label the vertical scale and to show .

500 mF Vc +

-

20

10

10

8 V time

Vc

ts

Problem 5A (10 pts): Transform the circuit below to the frequency domain by labelling each element showing all values in angle notation, e.g. X / Y. , and providing the angle in radians.

6

2 cos (10t + /2) A

4 sin (10t + /4) V

25 mF

0.02 F

0.2 H

1 H

Problem 5B (10 pts): The inductor (inductance L1) & resistor (resistance R1) at left are driven at frequency . The same impedance can be implemented using two circuit elements connected in series, as shown at right.

State each type of element (L, R or C), and its physical value in terms of the original values L1, R1 and .

L1 R1

Type of element: _________

Physical value: _____________________ ZA

ZB Type of element: _________

Physical value: _____________________

10

Problem 6 (20 pts): Find i(t).

Is(T) = 30 cos ( 10t ) A vs(t) = 30 cos (11t ) V

1 F

1 H

5 i(t) = ?

Problem 7 (20 pts): Write an expression for the VA, the complex voltage at node A, in terms of the values defined in the circuit below. You do NOT need to simplify this expression.

Is

2i

A

ZR ZL

ZC V1

i

ZC2

ZL2

VA + -

is(t) = cos (10t) A

20 mF

3 H

10 ZL

a

b

Problem 8 (20 pts): For the drive circuit below, the average power transfered from the AC current source into the load can be maximized by two series components (one resistor and either an inductor or capacitor).

8A: What are the two components physical values?

Resistor: _________________________ Capacitor / Inductor: __________________________

8B: If the same load was driven by the circuit above, except that the AC source were replaced by a 1A DC current source, how much average (steady state) power would be transferred into the load?

Problem 9 (20 pts) 9A & 9B (10 points each) What are the transfer functions H1() and H2() (Vout/Vin) for the two circuits below?

Vin1

RB

Vout1

Page 5/6

-

+

Rs RF

Vout2

+VCC

-VCC

Vin2

C

9C: (5 pts) Which values defined in the circuits limit the maximum transferred frequency, and how?

9D: (5 pts) Which values defined in the circuits limit the maximum and minimum transferred output voltage, and how?

9E: (5pts) If the output of the second circuit is connected to the input of the first, what is the new transfer function?

9F: (5 pts) Does this transfer function change of the order of the two circuits were reversed? Why?