ELEC 101, Spring 2005
Prof. Rich Kozick

## Homework 4

Date Assigned: Friday, February 4, 2005
Date Due: Monday, February 14, 2005 (for items 3 and 4 below)

1. Schedule for the week of February 7:
• No lectures on February 7 and 9.
• Lab on February 10 will be held from 12 - 3 PM in Dana 307 to make up for these lectures and to do Lab 4. Matt Sharp will teach this session. He will answer your questions for the exam, and he will work out example problems using nodal analysis. You may ask him questions about the problems on this homework assignment (but he will not work them out in detail!). If you want to meet with Matt at another time during the week, please email him at msharp@bucknell.edu
• Exam 1 will be on Friday, February 11 from 2-3 PM in BRKI 166. The exam is closed-book and closed-notes, but you should bring a calculator. The topics include Chapter 1 of the text, Homeworks 1-3, Labs 1-3, and everything we did in class through February 4 (except nodal analysis).

2. Reading: Please continue to study Chapter 2 in the Bobrow text, Sections 2.1 and 2.2 on nodal analysis. For the week of February 14, we will discuss Section 2.4 on operational amplifiers (op amps).

3. Bridge circuit: Recall the bridge circuit that we used in Lab 3 to detect a difference in temperature. Let us consider how we can calibrate the bridge to account for non-identical thermistors.

[CIRCUIT DIAGRAM IS NOT AVAILABLE IN HTML DOCUMENT.]

Suppose the thermistors RT1 and RT2 are not identical. At room temperature, RT1 = 5000 ohms and RT2 = 6000 ohms. At a higher temperature, RT1 = 3000 ohms and RT2 = 4000 ohms. Suppose that RA = sqrt(5000*3000) = 3870 ohms, but that RB is a potentiometer whose resistance can be varied from 100 ohms to 10,000 ohms.

(a) What value should RB have in order to "balance the bridge", i.e., set vout = 0 V, at room temperature? Please explain.

(b) If vout is a positive voltage, which thermistor is warmer? Please explain.

4. Nodal analysis: Please do problems 2.6, 2.7, 2.8, and 2.10 in the Bobrow text.
Thank you.