PHYS345 Final Exam          December 10, 1999

1.  Fun with op amps (5 points)

What does the following circuit do?   Subtractor

2.  Loading passive filters (15 points)

  1. Design a high-pass RC filter with a characteristic frequency of 80 Hz using a capacitor of 2.0 mF.   R = 1.0k

  2. What is the new characteristic frequency when the filter is loaded with 50 ohm?   1.67 Hz

3.  Digital Paranoia (20 points)

a.   Design a 3-bit, 5-state counter that cycles repetitively through the states 000, 001, 010, 011, and 100.

  D2 = Q1 AND Q0
  D1 = Q1 XOR Q0
  D0 = Q2 NOR Q0

b.   Indicate the behavior of the excluded states on the following state diagram.

  101 and 110 enter at 010; 111 enters at 100

4.  Too many batteries! (20 points)

  1. What is the current in the inductor a long time after the circuit has been formed?   200 mA

  2. What is the power delivered by the battery to the rest of the circuit?   1.08 W

  3. What is the current in the inductor a long time after the second circuit has been formed?   63 mA

  4. How long does it take for the inductor to change to its new current value?   180 ms

5.  Too many resistors! (20 points)

Find the values of Ro and Rs for the -6dB attenuator.   R0 = 16.7 ohm; Rs = 66.7 ohm;

6.  More digging through the past... (20 points)

Determine the numerical value of the current through the capacitor.   j 2.5 A

Last updated Dec. 19, 1999.
Copyright George Watson, Univ. of Delaware, 1999.