ELEC 101, Spring 2005
Prof. Rich Kozick

## Homework 3

Date Assigned: Friday, January 28, 2005
Date Due: Friday, February 4, 2005

1. Reading: Please continue to study Chapter 1 in the Bobrow text, and begin reading Chapter 2, Sections 2.1 and 2.2, on nodal analysis.

2. A certain bicycle lighting system uses a lamp bulb rated to absorb 20 W of power when it is on. If the system uses four 1.5-V "D" cells in series (for a total of 6 V) to run the system:
1. How much current flows through the lamp bulb when it is on?
2. What is the equivalent resistance of the lamp bulb when it is on?

3. Please solve the following problems in Chapter 1 of the Bobrow text.
1.30 (combine series/parallel resistors and use voltage dividers)
1.45 (dependent source)

4. Consider the voltage divider circuit shown below, where R1 = 2000 ohms and R2 = 3000 ohms. Please find the current, i, the voltage V2, and the voltage across the 2000 ohm resistor. Be sure to draw the circuit diagram in your solution, and label the polarity of the voltage across the 2000 ohm resistor and the direction for the current, i.

5. Consider the voltage divider circuit shown below, where Rsensor is a thermistor whose resistance is 1000 ohms at room temperature and 5000 ohms at body temperature.
1. If R1 has value 500 ohms, what is the value of the voltage Vsensor at room temperature and at body temperature? What is the difference in Vsensor at the two temperatures?
2. What value for R1 maximizes the difference in Vsensor at the two temperatures?
(We will work on this in Lab 3 on February 3.)

6. Design a current divider circuit that will produce a current division ratio of 0.5, so that half of the current flows through each branch. The current divider should draw less than 1 milliwatt (1 mW) of power when the input is a 1 A current source. Explain your reasoning.
Thank you.