ECE 20001 - ECE Fundamentals I - Fall 2019
Exam #2
October 10, 2019
Name:
Student ID:
PLEASE CIRCLE YOUR SECTION BELOW
Peroulis/Mayer (0002) – 9:30 am
Michelusi (0003) – 3:30 pm
Peleato-Inarrea (0005) – 11:30 am
Upadhyaya (0004) – 4:30 pm
Kildishev (0006) – 2:30 pm
Honor Pledge: I pledge that I will neither provide nor receive any
unauthorized aid during this exam and that I will only include my own work.
Honor Pledge (sign):
Instructions
• Exam Duration: 60 minutes.
• DO NOT START UNTIL YOU ARE TOLD TO DO SO.
• ON SCANTRON ADD: section number, answers, PUID, and signature
• Please have your PUID on your table.
• This is a CLOSED BOOKS and CLOSED NOTES exam.
• The use of a TI-30X IIS calculator is allowed, but not necessary.
• If extra paper is needed, use the back of the last page.
• Cheating will not be tolerated. Cheating in this exam will result in, at the minimum, an F grade on
this exam or for the entire course at the discretion of your professor. In particular, continuing to
write after the exam time is up is regarded as cheating.
• If you cannot solve a question, be sure to look at the others ones, and come back to it if time permits.
• When approximating, round to the closest whole number.
Potentially Useful Formulas
R
iL (t) = iL (∞) + [iL (t0+ ) − iL (∞)] e− L (t−t0 )
(1)
1
vC (t) = vC (∞) + [vC (t0+ ) − vC (∞)] e− RC (t−t0 )
1
L(i(t))2
2
1
WC = C(v(t))2
2
WL =
(2)
(3)
(4)
Potentially Useful Approximations
ln(2) ≈ 0.7
ln(3) ≈ 1.1
ln(4) ≈ 1.4
ln(5) ≈ 1.6
Outcomes
On exam #2, problems 1 through 4 provide evidence for satisfaction of ECE 20001 Learning Outcomes
(LO) (i) and problems 4 though 10 provide evidence for satisfaction of ECE 20001 LO (ii).
(i) An ability to analyze linear resistive circuits.
(ii) An ability to analyze 1st order linear circuits with sources and/or passive elements.
Exam Score
Q
LO
Pts
1
i
10
2
i
10
3
i
10
4
i,ii
10
5
ii
10
6
ii
10
7
ii
10
8
ii
10
9
ii
10
10
ii
10
Total
100
Score
ECE 20001
Exam 2
Question 1 [10 pts.]
What is the Norton equivalent representation of the linear circuit?
Io
Linear Circuit
+
Vo
–
IN (A)
VOC = 6 V
ISC = 2 A
RN (Ω)
1.
0
2
2.
2
2
3.
3
2
4.
6
2
5.
0
3
6.
2
3
7.
3
3
8.
6
3
9. None of the above.
Page 1 of 9
October 10, 2019
ECE 20001
Exam 2
October 10, 2019
Question 2 [10 pts.]
What is the value of the voltage Vo when V1 = 3 V and I1 = −1 A? Assume that there are
no independent sources within the linear circuit box.
+
V1
Linear
Circuit
+
−
Vo
-
I1
V1 (V)
0
1
3
I1 (A)
1
0
-1
Vo (V)
5
3
?
1. 1 V
2. 3 V
3. 4 V
4. 5 V
5. -1 V
6. -3 V
7. -4 V
8. -5 V
9. None of the above.
Page 2 of 9
ECE 20001
Exam 2
October 10, 2019
Question 3 [10 pts.]
What is the Thévenin equivalent representation of this circuit?
6V
+
−
2Ω
10 V
+
−
VTh (V)
RTh (Ω)
1.
1
1
2.
1
2
3.
1
4
4.
1
0
5.
13
1
6.
13
2
7.
13
4
8.
13
0
9.
2A
None of the above.
Page 3 of 9
2Ω
ECE 20001
Exam 2
October 10, 2019
Question 4 [10 pts.]
What is Vo under DC steady-state conditions?
1Ω
1H
+
5A
1F
2Ω
Vo
−
1. 5e
−t
3
V
2. 5e−3t V
3. 10e
−t
3
V
4. 10e−3t V
5. 0 V
6. 5 V
7. 10 V
8. 15 V
9. None of the above.
Page 4 of 9
ECE 20001
Exam 2
October 10, 2019
Question 5 [10 pts.]
How much magnetic energy is stored in the inductor at time t = 2 s?
(3t)u(t) V
+
−
1. 0 J
2. 1 J
3. 2 J
4. 3 J
5. 6 J
6. 9 J
7. 12 J
8. 18 J
9. None of the above.
Page 5 of 9
2H
ECE 20001
Exam 2
October 10, 2019
Question 6 [10 pts.]
What is the approximate value of the voltage vC (t) at t = 10 s?
2Ω
−
5u(−t) V
+
−
5F
vC (t)
+
1. -5 V
2. -4 V
3. -2 V
4. 0 V
5. 2 V
6. 4 V
7. 5 V
Page 6 of 9
ECE 20001
Exam 2
October 10, 2019
Question 7 [10 pts.]
Find the time constant τ .
15 Ω
+
12 H
2Ω
Vo
−
1. 1 s
2. 2 s
3. 3 s
4. 4 s
5. 1/3 s
6. 12 s
7. 17 s
8. 48 s
9. None of the above.
Page 7 of 9
0.25Vo
ECE 20001
Exam 2
October 10, 2019
Question 8-10 [10 pts. each]
Analyzing the circuit below, please find:
Question 8 – The approximate value of vC (1), to the closest whole number.
Question 9 – The value of vC (∞).
Question 10 – The approximate instance in time (t > 0) when the value of the voltage vC (t) is zero.
You must show all work. There is additional space provided on the next page with the
circuit redrawn.
t=1s
3Ω
t=1s
1Ω
5u(t) V
+
−
7Ω
+
−
+
vC
0.25 F
−
Question 8
Question 9
Question 10
1. -4 V
1. 7 V
1. 1 s
2. -3 V
2. 3 V
2. 2 s
3. -2 V
3. 2 V
3. 3 s
4. -1 V
4. 1 V
4. 4 s
5. 1 V
5. 0 V
5. 5 s
6. 2 V
6. -1 V
6. 6 s
7. 3 V
7. -2 V
7. 7 s
8. 4 V
8. -3 V
8. ∞ s
Page 8 of 9
2V
ECE 20001
Exam 2
Extra Space to Work
3Ω
t=1s
October 10, 2019
t=1s
1Ω
5u(t) V
+
−
7Ω
+
vC
0.25 F
−
Page 9 of 9
−
+
2V