ELEC 101, Spring 2005

Prof. Rich Kozick

Prof. Rich Kozick

**Reading:**The relevant reading is in Sections 3.1, 3.2, and 3.3. We will not cover every topic in the text, and we will emphasize capacitors more than inductors. The concept of a*time constant*is very important.- Please solve the following
problems in Chapter 3 of the Bobrow text.
- Problem 3.7.
- Problem 3.28. What is the
*time constant*for this circuit? - Repeat problem 3.28 for the case that the switch is
*opened*for t < 0, and the switch is*closed*for t >= 0. What is the time constant for the circuit in this case?

- Please solve problem 3.48 in the text.
Note that the voltage source has value 0 volts for t < 0,
and V volts for t >= 0.
Thus it is equivalent to "closing a switch" at time t = 0
to connect an ideal source with value V volts.
Hint: Write KCL at the "-" input of the op amp. Use the ideal op amp assumptions.

Also answer the following questions for this circuit.

- What is the time constant?
- Sketch v
_{o}(t). - After a long time, i.e., t >> 0, does this look like an inverting amplifier? Please explain.

- Please analyze the RC circuit that we used in
Lab 6 for the following cases.
Assume that V
_{s}= 12 V, C = 1 microfarad, R = 1,000 ohms, and R_{s}= 100 ohms.- Assume that the switch was closed for a long time, and that it is opened at time t=0. Find the expression for v(t) and make a sketch of the voltage versus time. Label the voltage and time axes on your plot, and indicate the value and location of the time constant on your plot.
- Now assume that the switch is initially opened, and that the
capacitor is initially uncharged (i.e., v(0) = 0 V).
Suppose that the switch is
*closed*at time t=0.

Find the expression for v(t) and make a sketch of the voltage versus time. Label the voltage and time axes on your plot, and indicate the value and location of the time constant on your plot. - Why is the time constant different for the two cases?