Download EET 104 Quiz #1 January 31, 2005

EET 104
Final Exam
May 9, 2005
Name: _________________________________
(This test consists of TEN problems)
You are required to do 6 of these problems
All problems are worth an equal number of points
This is an OPEN TEXT CLOSE NOTES TEST.
Please show all working for credit!
Correct units are necessary for full credit!!
Feel free to solve the problems of loose blank paper, but make sure your name is on every
sheet of paper you intend me to grade!!!
I wish you all the best in this exam.
1. Sketch the waveforms for the following sets of equa0-tions, and state which
waveform leads and lags in each case.
a) v = 7sin(wt + 50o); i = 10sin(wt - 10o)
b) v = 4cos(wt + 30o); i = 4sin(wt - 45o)
c) v = 6sin(wt); I = 2.5cos(wt+90o)
2. For the circuit in Figure 1 below:
a) Determine the time constant of the circuit when the switch is thrown to
position 1.
b) Write the mathematical equations for the voltage, vc and the current, ic, after
the switch is thrown to position 1.
c) Write the mathematical equations for the voltage, vc and the current, ic, if the
switch is thrown to position 2 at t = 60ms.
d) Write the mathematical equations for the voltage, vc and the current, ic, if the
switch is thrown to position 3 at t = 150ms.
e) Sketch the waveforms for ic, and vc from 0 to 180ms.
Figure 1
3. Solve the following problems using Kirchoff’s current law:
a) Find I1, I2, I3 and I4 in Figure 2 below.
Figure 2
b) Find the voltage, V and the current, I in Figure 3 below..
Figure 3
4. For the circuit in Figure 4 below:
a) Find V and I
b) Find the energy stored in each capacitor and inductor.
Figure 4
5. Solve the following
a) A 4-hp motor has an efficiency of 95%
I. Find the power input in Watts.
II. Find the power (in Watts) lost or stored in the system. Find the
input current if 150v was applied to it.
III. Find the resistance of the motor.
b) If 31.21 x 1019 electrons pass through a wire in 5 seconds and convert 15J of
energy:
I. Find the potential drop across the wire.
II. Find the resistance of the wire.
III. Find the power absorbed by the wire.
6. Answer the following in your own words as much as possible (no equations please)
a) Define Power
b) Define Resistance
c) Define Voltage
d) State Ohm’s law (please don’t use the word “equals”)!
e) Describe the relationship between inductance and capacitance (that is,
compare and contrast them)
7. For the circuit in Figure 5 below:
a) Write the equations for the inductor voltage and current if the switch is closed
at t = 0;
b) At what time is the inductor current = 5mA
c) At what time is the inductor voltage = 5V
Figure 5
8. A gold bar has a length of 25 inches, a width of 3 inches, and a height of 2 inches:
a. Find the resistance at room temperature using circular mils resistivity
b. Find the resistance at room temperature using metric resistivity and
compare you solution to (a).
c. Find the resistance at t = 0oC and t = 10oC
9. Find Is, I1, I3 I4, Va, Vbc in Figure 6 below.
Figure 6
10. Do the following:
a) Sketch the waveform for the average current if the voltage across a 1μF
capacitor is as shown in Figure 7 below.
Figure 7
b) Sketch the inductor current if the voltage is as shown in Figure 8 below. The
value of the inductance is 40mH
Figure 8