Ohm's Law

Ohm’s Law
Lab Report Number Three
Quyama T. Wheeler
@02669651
Partner: Munah Kaye
Amber Frazier

Objective: To demonstrate Ohm’s law and to determine the resistance of a given resistor.
Theory: Ohm’s law is the assertion that the current through a device is always directly proportional to the potential difference applied to the device. Electric current is the moving of charges from a higher potential to a lower potential. Wires of different material (a copper wire versus a silver wire, for example) will produce different currents, even if applied the same potential difference. This phenomenon, this characteristic respectful to each type of material is known as resistance.
Apparatus:
-two multi-meters (set on the 20mA and 20 V scale)
-unknown resistor board
-Extech instruments (0-18 Volts) Power Supply
Procedure: A circuit connecting the resistor board, the voltmeter and the milli-ammeter is assembled. The 20 milli-ampere range is selected on the ammeter and the 20V on the voltmeter. The power cord is then plugged into an electrical outlet and the unit is turned on. The experiment begins at 15 volts. The voltage and current are both recorded and these steps are repeated successively in two volt increments. A graph of I as a function of V is plotted and fit with a straight line, the slope of which equals the resistance of the resistor. Repeat the same process for resistors seven and nine, and then for the circuit in series and in parallel.
Calculations and Results:
Equation: V = RI
Resistor 2
Reading
Current (I)
Voltage (V)
1
12.21
15
2
10.62
13
3
8.98
11
4
7.35
9
5
5.69
7
6
4.07
5

Resistor 7
Reading
Current (I)
Voltage (V)
1
2.86
15
2
2.48
13
3
2.09
11
4
1.71
9
5
1.33
7
6
.94
5

Resistor 9

Reading
Current (I)
Voltage (V)
1
7.15
15
2
6.21
13
3
5.24
11
4
4.29
9
5
3.33
7
6
2.37
5

Resistors 2 and 7 in Series
Reading
Current (I)
Voltage (V)
1
2.30
15
2
2.00
13
3
1.68
11
4
1.38
9
5
1.06
7
6
.75
5

Resistors 7 and 9 in Parallel
Reading
Current (I)
Voltage (V)
1
10.05
15
2
8.68
13
3
7.36
11
4
6.06
9
5
4.69
7
6
3.38
5

The currents and voltages of the resistors are recorded in the above charts. In the attached graph, I versus V is plotted, the resulting slope of the line they produce equals the resistance.
Conclusion: The objective asked for a demonstration of Ohm’s law and to determine the resistance of a given resistor. Ohm’s law was successfully demonstrated using the equation V=RI. It was expected that all of the resistances would fall into a straight line because Ohm’s law states that the current through a device is always directly proportional to the potential difference applied across the device. That all of the points (the resistances of the recorded currents and voltages) fell into a straight line when graphed proves the consistency of the equation. The resistances of the given resistors were also successfully calculated. The resistance is equal to the slope of the line of Current versus Voltage, shown in the attached graph.