Laboratory Experiment

Measuring Resistances

Let's start by making one resistance measurement.

Get a resistor. A one kW resistor would be good. You can tell it is a one kW resistor by the stripes. They should be brown-black-red in that order from the end, as shown at the right.

You are now ready to measure the resistance. Connect your resistor to an ohmmeter as shown at the right. Don't get uptight about which lead goes on which end of the resistor. It doesn't matter. (The resistor is a bilateral element and should be the same either way!) You should see a reading in the window, and that reading should be in the vicinity of one thousand ohms. Click here for the lesson on setting up an ohmmeter. Here are the connections you make. They're simple enough.

Take the measurement now! Then reverse the leads to check the claim above by measuring the resistance with the opposite lead connections.

The Resistor Color Code

You probably wondered about those stripes on the resistor. There is a color code that lets you tell what value the resistor has. Here's what's important.

This resistor is 1000 ohms = 10x10²

Notice how cleverly we put certain parts of the result in bold text and colored it. The bolded text corresponds to the stripes, and the colors are shown on the bold text. Here is the color code.

0	Black	Black
1	Brown	Brown
2	Red	Red
3	Orange	Orange
4	Yellow	Yellow
5	Green	Green
6	Blue	Blue
7	Violet	Violet
8	Gray	Gray
9	White	White

Given a resistor, to calculate the value of the resistance you use the three stripes. (If there are four stripes, just use the first three. The last stripe tells you how accurate the resistance value is.) Here is the algorithm.

The first stripe is the most significant digit, X, in XY x 10^Z.
The second stripe is the next digit, Y, in XY x 10^Z.
The third stripe is the exponent in XY x 10^Z.

Here are some examples/problems.

Problems

P1. For the resistor at the right answer the following questions. Note, for this problem, if you do not get a grade of 100 you answered incorrectly. Now, what is the first digit on the resistor's set of stripes?

P2. What is the second digit on the resistor's set of stripes?

P3. What is the exponent?

P4. What is the value of the resistor?