Lab 2: DC Circuits
Reading Assignment
1. Hands-On, Ch. 2, up to 2.2.1.
2. HH Lab Manual Class 1 and Worked Examples (pg 3-23 of lab manual)
3. HH Text pg 1-19 (through sec 1.9), first part of sec 1.11
4. How to read resistors: http://www.elexp.com/t_resist.htm
5. Easy steps to calculating Thevenin Equivalent (see bottom of page):
http://www.allaboutcircuits.com/vol_1/chpt_10/8.html
Additional background:
A. I-V Curves
Source: Curtis
The I-V curve of a circuit element or device may be obtained in the following
manner. First, the element is connected to an external power source such as a
variable voltage power supply. Next, the current through the device, I, and the
voltage across the device, V, are measured. The external power supply is then
varied so that I and V are changed and the new values are measured. This
procedure is repeated and the points are plotted on a graph of I vs. V. The curve
that connects these points is called the I-V curve for the device being tested.
Linear devices have I-V curves that are straight lines. For many devices the
response, or current through the device, is proportional to the input, or voltage,
across the device over a broad range. These I-V curves obey Ohm’s law:
V = IR. (1)
Devices that obey Ohm’s law are called resistive elements. Other elements may
have non-linear I-V curves or response. In some cases the response is not even
symmetric about zero.
B. Power Dissipation
For direct current, power dissipation can always be written as:
P = V I. (2)
This is just the potential energy change per charge (V) times the amount of
charge per second (I) passing through. For resistive elements, this reduces to:
P = V I = I2R =V2 / R. (3)
Either of these forms can be used for resistors. For non-linear devices, you must
use (2).