Ohm's+Law-+Lekha+Vuppalapati,+Ellen+Apple,+and+Chase+Stockton

Title of Lab: Ohm's Law Inquiry Lab

Researchers: Lekha Vuppalapati, Ellen Apple, and Chase Stockton

Research Question: Experimentally find the relationship between the voltage across the Ohmic device and the current flowing through the device.

Research: Electric current is a flow of electric charge. Electrons passing through a wire create this flow of electric charge. As the voltage increases, this flow of electrons passing through the wire will also increase, leading us to believe that an increase in one will yield an increase in the other.

Hypothesis: The current and voltage are directly proportional to one another.

Materials: Voltage source, ammeter, voltmeter/multimeter, resistor, lead wires, pin connectors, and alligator clips. Note the resistor had colored bands in this order: Brown, Black, Black, Gold

Constants: Length of wire Variables: Voltage of volt source, voltage across resistor, current,

Procedure: 1) Using either pin connectors or alligator clips (whichever is more applicable), hook up the voltage source to the ammeter. 2) Hook up the ammeter to the resistor. 3) Hook up the resistor back into the voltage source to complete the circuit. 4) Using the voltage source, change the voltage of the circuit to a unique value. Be careful to not melt the resistor. 5) Note the current going through the circuit by reading the ammeter. 6) Using the voltmeter/multimeter and its lead wires, measure the voltage from one end of the resistor (between the ammeter and the resistor) to the other (between the resistor and the voltage source). 7) Note the voltage across the resistor. If it is negative, switch which lead wires are touching which ends of the resistor. 8) Repeat steps 4-7 until you have gathered a sufficient amount of data.

Data: Even though we modified the voltage on the voltage source, this was to change the current going through the circuit to reach a particular value. At this current, we measured the voltage across the resistor. Since we modified the current going through the circuit and measured the voltage across the resistor, the current is the independent variable and the voltage across the resistor is the dependent variable. Because of this, it should also be noted that the "Voltage" in both the table (above) and the graph (below) is the voltage across the resistor as measured by the voltmeter.

Data Analysis:

The y-intercept is at about .031 V, which is within our margin of error for the voltage of about .05 V. As the x-intercept also falls within the margin of error of the current (.005 A), we can reasonably conclude that the line of best fit crosses through the origin. This makes sense, both theoretically and realistically: if no voltage is going across a wire, then nothing should be making the electrons move through it (and hence no current). Also, one of our data points was (0 A, 0 V), showing that realistically the relationship between the two should pass through the origin. The graph appears to be linear, such that the voltage across the resistor is about 9.3 V/A times the current going through the resistor.

Conclusion: Because the graph relating voltage to current closely follows a linear pattern and goes through the origin, we can reasonably conclude that they are directly proportional to one another. Using the following resistor color chart and Ohm's Law, the actual proportionality constant relating voltage to current can be calculated: The color of our resistor was Brown-Black-Black-Gold, making our resistor have a resistance of 10*1 ± 5% Ω. This leads to a minimum possible percent error of 2.1% and a maximum possible percent error of 11%. Even though this percent error may be too large to consider this data to be scientific evidence thoroughly supporting Ohm's Law, it certainly does not show that Ohm's Law is incorrect, as they were indeed directly related to one another. The source of this error probably lied in the wire connections. Some wires were loose in the voltage source and in the ammeter, we didn't make sure we tested the same exact points at either end of the resistor to see the voltage, and the wires were connected to one another, sometimes loosely. If someone were to repeat this lab, we would recommend the following: 1) Wire everything up as simply and as neatly as possible (don't have wires connecting to other wires connecting to machines). 2) Attach the voltmeter/multimeter to both ends of the resistor using something like alligator clamps instead of using lead wires (so you don't have to hold them there constantly). 3) Ensure that the wires are completely and utterly connected to the machines such that they aren't loose. 4) Use a resistor with a lower tolerance.