NAME:___________________________
Recitation section number (or day/time):___________________________
PHYS345 Final Exam December 17, 1998
This is a closed book exam. One 3"x5" note card is permitted; this card should be turned in with your exam papers.
Programmable calculators and graphing calculators may be used during this exam.
Since this exam booklet may be separated for grading; it is important to:
Show ALL work on problem sheet and only on that sheet.
Please read questions carefully.
Credit may be lost inadvertently if solutions are not neat and orderly.
Be careful with units, signs, and significant figures.
1. Motors and dimming lights (20 points)
Use what you have learned about ac circuits this term to understand some of the issues involving power distribution to industrial motors. Quoting from the textbook:
Large motor starting currents drawn through transformer and line impedances drop the voltage at the motor and therefore for other loads fed from that line. A sufficiently lowimpedance transformer and line must be provided to keep the load voltages within established tolerances.
In the following circuit schematic assume that the transformer reactance is 0.15 ohm and the line reactance is 0.10 ohm.
2. Digital Comparator (15 points)
A  B  C 
0  0  0 
0  1  0 
1  0  1 
1  1  0 
3. Too many batteries! (20 points)
A 9.0 V lithium battery (internal resistance 18 ohm) has been connected to a
real inductor (inductance of 1.0 H and resistance of 27 ohm) as shown.


A 1.5 V AA cell (internal resistance 0.6 ohm) is added in parallel
to the 9.0 V battery and inductor as shown.

4. Gray counter (15 points)
Determine the state diagram for this twobit counter.  
How would you reconfigure the counter to reverse the sequence determined above? (Show all work!) 
5. Realworld differentiator (20 points)
The following differentiator circuit has been designed for a signal conditioning
application. The resistor has a value of 100k and the capacitor
has a value of 1.0 microfarad.





6. The 555 Timer (15 points)
The 555 integrated circuit is an extremely useful package of analog and digital electronics for building timing circuits. In the circuit shown, the 555 is being used to create a digital clock signal.  
The following text has been lifted from the manufacturer's literature:
That is, the charging time t_{H} is the time it takes to charge the capacitor from 5 V to 10 V when connected to 15 V through the resistance R_{A} + R_{B}. (V_{CC} = 15 V has been assumed.) The discharging time t_{L} is the time it takes to discharge the capacitor from 10 V to 5 V when connected to ground through the resistance R_{B}.
From the information given above, determine a formula for the frequency of the clock.
Check its validity against the timing diagram shown below.

