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ECE 201 Exam 2 10/19/
General Instructions:
- There are 15 multiple choice questions. Each is worth 6 2/3 points for a total exam score of 100 points. The order of problems is random.
- Answers to the multiple choice questions must be marked correctly on your scantron. For purposes of determining your score, it is only the scantron choices which count.
- Fill in your name, student identification number, and division number in the appro- priate places on the computer scantron form.
Division Class Time Instructor 0001 1:30 pm Prof. Qi 0002 4:30 pm Prof. Chen 0003 8:30 am Prof. Krogmeier 0004 4:30 pm Prof. Clark
- Fill in the correct exam version number in the appropriate place on the computer scantron form. This exam booklet is for:
Exam Version A
- The exam is closed book and closed notes. No scrap paper is permitted. No calculators are allowed.
- If you finish the exam during the first 55 minutes, you may turn it in and leave. During the last 5 minutes you must remain seated until we pick up scantrons from everyone.
- Cheating is wrong. If you are caught cheating, you will fail the course and be reported to the Dean of Students.
Problem 1. Consider the Thevenin equivalent of the circuit below with respect to terminals a–b. The open circuit voltage across terminals a–b is:
(1) 1 V (2) 2 V (3) 3 V (4) 4 V (5) 1.5 V (6) -2.5 V (7) none of these
2 ix
ix
a
b
Answer = #
Problem 2. Consider the Thevenin equivalent of the circuit below with respect to terminals a–b. The Thevenin equivalent resistance seen at terminals a–b is:
(1) 1 Ω (2) 2 Ω (3) 3 Ω (4) -3 Ω (5) -2 Ω (6) -1 Ω (7) 2.5 Ω
2 ix
ix
a
b
Answer = #
Problem 4. The circuit below models the scenario where one is trying to display a square wave from a function generator on an oscilloscope in the laboratory. We are using a 50 Ohm square wave generator to create a ±5 V square wave v(t) with 3 different frequencies. The frequency f 0 of the square wave is related to its period T 0 by f 0 = 1/T 0. The output of the square wave generator is connected to the input of the oscilloscope using a section of coaxial cable. Models for each of the components of the system are connected as shown. Measurements of 3 different frequencies are taken. The resulting oscilloscope voltages vscope(t) are shown as the three superimposed Traces in the figure below the circuit. Note that the oscilloscope time scale is adjusted for each measurement such that exactly 2.5 periods are displayed in each case. From the possibilities below pick the most reasonable answer for the frequencies corre- sponding to Traces 1, 2, and 3.
f 0 ,T race 1 = 500 MHz f 0 ,T race 2 = 50 MHz f 0 ,T race 3 = 5 MHz
f 0 ,T race 1 = 500 KHz f 0 ,T race 2 = 50 KHz f 0 ,T race 3 = 5 KHz
f 0 ,T race 1 = 5 MHz f 0 ,T race 2 = 50 MHz f 0 ,T race 3 = 500 MHz
f 0 ,T race 1 = 50 MHz f 0 ,T race 2 = 500 MHz f 0 ,T race 3 = 5 MHz
f 0 ,T race 1 = 5 KHz f 0 ,T race 2 = 50 KHz f 0 ,T race 3 = 500 KHz
f 0 ,T race 1 = 50 KHz f 0 ,T race 2 = 500 KHz f 0 ,T race 3 = 5 KHz
f 0 ,T race 1 = 50 GHz f 0 ,T race 2 = 500 GHz f 0 ,T race 3 = 5 GHz
20 pF
model of oscilloscope input
1 MΩ
30 pF vscope(t)
model of coaxial cable
v(t)
50 Ω
model of square wave generator
−5 0 0.5 1 1.5 2 2.
−
−
−
−
0
1
2
3
4
5
Time normalized by period, i.e., t/T 0
vscope
(t) in Volts
Trace 1 Trace 2 Trace 3
Answer = #
Problem 5. The circuit shown is in the steady state with the switch closed. At time t = 0 the switch is opened. Find the current i(t) for t > 0.
(1) 4 − 6 e−^50 t^ A (2) 10 − 2 e−^20 t^ A (3) 3 + 2e−^30 t^ A (4) 3 − 2 e−^20 t^ A (5) 2 + 10e−^30 t^ A (6) 4 + 6e−^50 t^ A (7) 10 − 5 e−^20 t^ A
100 V
0.5 H
t = 0
i ( t )
Answer = #
