Review Exercise: Using a Multimeter

Purpose:

The purpose of this lab is to learn how to prevent a multimeter from burning out its fuse by doing resistance, voltage, and current test.

• Resistance Test

1. First we set the multimeter to read resistance when its two probe do not touch anything, the reading from the multimeter is zero ohm.
2. Touching the two probes together, the reading of the multimeter is 1 ohm since the metal tips are conductors.
3. Then we need to grab a set of four different resistors and record the measured and theoretical values. Here is the way to figure out the color:

   
       original source above is from  http://www.afiata.com/how-to-read-resistor-color-codes/.

   First resistor we choose is "Red orange brown", so resistance value from colors is 230 ohm, and
its measured value from multimeter is 218 ohm. Next, the color of resistor is Orange orange red", so the resistance value from its colors is 3300 ohm, and its measured value from multimeter is 3290 ohm.  Third, the color are "Orange, orange, brown"; therefore, the resistance value from its colors is 330 ohm, and its measured value from multimeter is 329 ohm. Finally, we choose "Red, black, red", so the resistance value from colors is 2200 ohm, and its measured value from multimeter is 2010 ohm. Notice that there is a color code at rightmost location, and the color of all tested resistors are gold, which tell us that the error for the certain resistor is within five percent.

• Voltage Test

1. Set the multimeter to read DC voltage.
2. Use two probes of the multimeter to touch a 9 volts battery, the measured value is 9.10 V.
3. Testing wall wart adapter, we get 23.0 V. (Output from label is 18V) If we use two alligator clips to attach a 150 ohm resistor across two multimeter terminal the voltage we measured is still 9 V.
4. Make a circuit as shown in figure 1. 

Figure 1. An LED circuit

The measured voltage across LED is 2.13 V. The voltage of the battery to the sum of the voltage drops across the resistor and the LED is the same.

• Current Test

1. Set the multimeter to read DC current and make a circuit as figure 1.
2. To measure the current of the circuit, the multimeter has to insert the circuit as in series. The measured current is 15.9 mA.