PHYS345 First Midterm Exam October 28, 1999

1.

  1. What would be the source voltage needed to get 25 W at the 8 ohm speaker?     28.3 V

  2. What would the power be if a 4 ohm speaker is connected instead?     22.2 W

  3. Find the value of Is.     1.25 A

  4. What if the 2 ohm and 6 ohm are interchanged?     no difference

  5. Does the circuit become inductive or capacitive?     capacitive


2.

  1. What value for the so-called signal-to-noise ratio should be reported to your boss?     20 dB

  2. Design and sketch the circuit required.     1.5 mF input capacitor, followed by 500 ohm resistor to ground. Tap output from between the two circuit elements.

  3. What new signal-to-noise ratio can be achieved by using this filter?     28 dB


3.

  1. What power is delivered by the voltage source?     300 W - j 1700 VAR

  2. What power is dissipated by the motor?     300 W + j 230 VAR

  3. What capacitance do you need to correct the power factor back to unity?     43 mF


4.
  1. How much time does the youngster have to vacate the premises?     3.3 sec

  2. Now how much time expires after switch closure until the fuse is ignited?     2.5 sec


5.

  circuit
A
  circuit
B
terminal
voltage
  1.64 V   1.10 V
current
through
9V battery
  0.41 A   -0.56 A


"http://www.physics.udel.edu/~watson/phys345/exams/mid1-99f-ans.html"
Last updated Nov. 3, 1999.
Copyright George Watson, Univ. of Delaware, 1998.