EE 200
Prof. Rich Kozick
Spring, 1997

EE 200: Homework Assignment #5

Date Assigned: Wednesday, February 12, 1997
Date Due: Monday, February 17, 1997 at 8 AM

Exam 1: We will have our first exam on Wednesday, February 19. The exam will include the material covered in class and lab through Monday, February 17. The relevant chapters in the text are 1, 2, and 3. The main topics are: concepts of charge, current, voltage; Kirchhoff's current and voltage laws; resistance and Ohm's law; power; voltage divider and applications of voltage divider; Thevenin equivalent model for voltage sources; maximum power transfer; and nodal analysis.

The exam will be closed-book and closed-notes, but you will be allowed to bring one sheet of 8.5 inch by 11 inch paper, on which you can write whatever you'd like on one side.

Problems:

1. Suppose you have a real (non-ideal) voltage source with 10 ohm internal resistance, as shown below. The source is used to light a bulb, as shown.
   1. What value of resistance should the bulb have in order for it to shine as brightly as possible?
   2. How much power is dissipated by the bulb when its resistance has the value you specified in part (a)?
   3. How much power is dissipated by the bulb when it has resistance 1 ohm? What about 100 ohm?

   [More questions on back of page.]

2. On Homework #4, you used a voltage divider to convert an ideal 10 volt source into a 5 volt source. A solution is shown in circuit (A) below. Please find the Thevenin model for circuit (A). That is, find and in circuit (B) so that both circuits have the same voltage and current behavior at their terminals.

   Hint: Find the open-circuit voltage and short-circuit current in circuit (A).

3. Suppose that a voltage source (also called a power supply) is to be designed such that it provides 12 volts when its terminals are open-circuited (nothing connected between them). In addition, the voltage source must be able to provide at least 70 watts of power to a load. What is the maximum value of in the Thevenin model for this source?

 
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