1 2 3 4 (tolerance)

EE 101 Lab Exercise 1: Resistors

1. Take the resistors out of their bag. Make sure there are 8 of them. Make a chart with headings like the one below. List each resistor by its color bands (see column "Resistor Color Bands" below). Using the color code scheme outlined in class, determine the values for each resistor and write these in the column under "Color Code Value". When you are through with this, measure the resistor values with a multimeter (set to ohms). Be sure not to touch the leads on the resistor while you are measuring its value, because you will, in effect, be adding your own resistance (in parallel) to that resistor, and this will affect the answer you get. All the resistors in this lab have a tolerance of 5% (as indicated by the gold band on the end). Indicate whether or not the resistors are within tolerance in the last column. When you are finished, put the resistors back in their bag. You will be using these again later in this lab.

Color Bands Value Measured Value WithinTolerance?

              br-blk-r-(gold) 1 KW             ?                    (yes or no)

Exercises 2 - 5 require you to build circuits on a protoboard. For all of these circuits, proper breadboarding technique will be expected. This includes using the built-in runners on the breadboards when applicable, using wire cut to proper lengths, and using a proper amount of breadboard space. In short, the circuits you build should be "readable." Any circuit that does not demonstrate proper breadboarding technique will not be graded.

2. Using resistors and wire, build the circuit from Exercise 2 in the pre-lab. Power does not need to be applied to this circuit. Use the multimeter to measure the equivalent resistance (Req) of the circuit. What value do you measure, and how does this compare to the value we calculated in class? (Perform a percent difference between the measured value and the expected value of the equivalent resistance.)

3. Follow the instructions from number 2 above for Exercise 3 in the pre-lab.

4. Build the circuit from Exercise 4 in the pre-lab. Ask one of the lab assistants to check your circuit before applying power to it.

a. Using a voltage meter, measure Ia by measuring the voltage drop across the resistor, and then calculating the current. Do this first with the meter probes one way (red/black), then the other (black/red). Write down your answer for Ia (positive answer). In the same way, measure and record the value of Ib.

b. Now, measure Ia and Ib using a current meter. Record the values. Are the values you obtained using the current meter significantly different from the ones you calculated using Ohm’s Law (from part 4a)?

c. How close are your measured currents (using the current meter) to the values you calculated in the pre-lab (do a percent difference)?

d. Determine the source current (Is) using a current meter. Is Ia plus Ib equal to Is? What law is demonstrated here?

5. Build the circuit from Exercise 5 in the pre-lab. With the help of the multimeter, adjust your source voltage to as close to 15V as you can make it. Record the actual value you measure for Vs. Ask an assistant for help in doing this, if you need, and as always, ask one of the lab assistants to check your circuit before applying power to it. With the multimeter, measure V1 and V2. Do these two values add up to equal the value of your source voltage? What law is demonstrated here?

Additional question

The equivalent resistance values you measured in 2 and 3 above were probably not exactly what we had calculated in class. What reasons can you think of for the difference?