Measure the current the circuit illustrated the diagram the right

Lab:	2

Lab 2: Resistance and Ohm’s Law

 Determine the tolerance of a resistor using its color code.

 Calculate the percent of variation between a nominal value and a measured value.

1 x		1 x

Discussion:

Variable Power Supply Fluke 179 or equivalent Digital Multi-Meter
Prototyping board
Assorted Resistors

Georg Ohm discovered in 1827 that there is a direct relation between the voltage and current in a circuit. Ohm’s Law, named in his honor, states that the current through a conductor is directly proportional to the potential difference applied across the conductor. Georg Ohm originally stated in 1827 that the conductivity of the conductor represented the proportionality constant relating the voltage across and current through it. As a result, Ohm’s Law was originally expressed as I=σV , where σ represents the conductance of the material. Later, when

resistance was defined as the reciprocal of the conductance, Ohm’s Law was restated in its current form:
V=IR This Lab is intended to introduce the resistor color code and to demonstrate Ohm’s

Table 1: Measured and Calculator Resistor Values
Color Band	Nominal	Tolerance	Value Range	Measured	Variation
EX: Red/Purple/Orange/Gold	27 kΩ Value	±5% (%)	25.7kΩ–28.4kΩ	26.2 kΩ Value	2.9 % (%)
Red/purple/red/gold	2700Ω	5	2565-2835	2655	1.67%
	680Ω	5	646-714	667	1.91%
	1MΩ	5	.95M-1.05M	.983M	1.7%
	10kΩ	5	9500-10500	9830	1.7%
	680Ω	5	646-714	667	1.91%
Yellow/violet/black/gold	47Ω	5	44.65-49.35	46.2	1.7%
Brown/green/brown/gold	150Ω	5	142.5-157.5	147.4	1.73%
	1.6MΩ	5	1.52M-1.68M	1.591M	0.56%
	470kΩ	5	446.5-493.5	467.5k	0.53%

2.

3. Use the Digital Multi-Meter to measure each resistor and record the measured value in the corresponding column of the table. Refer to the diagram to the right or the User Manual to properly measure resistance.

Tip:

	Determine the percent of variation (error) between the nominal value and the measured value using the formula:


	Use the DMM to measure the resistance of the 1 MΩ resistor using the same method

described in step 3 above. Record the measurement in the space provided.

	Measurement :
7.
7.

	Measurement :
8.	Select a resistor with a red multiply band and use the DMM to measure its resistance using

the method described in step 4 above.

	Measurement :	2.655kΩ
9.
9.	Measurement :

11. Change Vs to 5 V and Repeat Step 10.

Table 2
Nominal Voltage			Measured Voltage	Measured Resistanc e		Variation (%)
15 V	1 kΩ	15 mA	15.56	.996	15.65	-4.33%
15 V	2 kΩ	7.5mA	15.56	1.961	7.97	-6.267%
15 V	5.6 kΩ	2.67mA	15.56	5.496	2.85	-6.74%
15 V	22 kΩ	0.682mA	15.56	21.61	.74	-8.5%
5 V	1 kΩ	5mA	4.965	.996	4.99	.2%

5 V	2 kΩ	2.5mA	4.965	1.961	2.55	-2%
5 V	5.6 kΩ	0.893mA	4.965	5.496	.92	-3.023%
5 V	22 kΩ	0.227mA	4.965	21.61	.24	-5.73%


13. Measure the voltage applied to the circuit and record it in the second column of Table 2.

Questions:

Part 1

3. How much did your measurement vary between steps 6 and 7? Which measurement was more accurate? Explain your answer.

The variation was by 287,000 ohms because the addition of the the fingertips on the ends of the resister makes the human body into an additional resister in parallel to the 1MΩ resister which brings the resistance down.

Variation goes up as circuit resistance increases and the voltage is fixed. Also the current decreases as the resistance in the circuit increases.

6. Explain why measured component values are preferred to nominal values when performing circuit calculations.

The source of the variation is due to the additional resistance added to the circuit by the insulaters that are a part of the DMM and also the additional resistance of the operator’s body as well as the insulator surrounding the DMM leads. The variation can be minimized by using leads with little contact with natural resisters, as well as keeping hands free from the leads during measurement and using more high technical DMM’s with better accuracy.