DC Circuit lab report

Accelerated Studies in Physics and Chemistry Laboratory
DC Circuit Lab

Author: Shannon K. Smith
Team Members: Caroline Kerley, Maegan Skinner
Date of Experiment: February 2, 2011
Date Report Submitted: February 25, 2011
Class: Accelerated Studies in Physics and Chemistry, D Block
Mr. Mays, Instructor

Purpose Statement

The purpose of this experiment was to accurately predict the voltages and currents of a DC multi-resistor circuit.

Background

The theories that this experiment was based on, both discovered by Kirchhoff in 1845, were the Junction Law and the Voltage Drop Law. The Junction Law states that the sum of the currents entering a node equals the sum exiting a node and the Voltage Drop Law states that around any loop the sum of the voltage rises equals the sum of the voltage drops. These laws were used to calculate the voltages and currents in the circuit. Ohm’s law was discovered by George Ohm in 1827. Ohms law states that V=IR. This law was used to calculate to predicted currents and voltages.

The team was given a breadboard and four resistors of different resistance and constructed a multi resistor circuit. The team experimented with the materials and discovered how to use the materials properly and then measured the currents and specific voltages. With that, the team calculated the Req for the predicted and experimental Ohms.

Experimental Procedure

The following equipment and materials were used in this experiment:

precision resistors (4)
Digital Multi Meter (1)
DC power supply: Flinn Battery Eliminator AP5375 (1)
aligator clamps (2)
bread board (1)
banana plugs (2)

The team was given the equipment and materials and experimented with how to use them properly. A schematic of the placement of the resistors was made and then transferred onto the breadboard. The team then calculated the experimental resistors, currents and voltages. The team then calculated the predicted values.


Results

The results for the current, voltage and resistance are displayed in Table 1.
Table 1
1 2 3 4
Experimental Current 1.4600 mA 1.0200 mA 0.4200 mA 1.4600 mA
Experimental Voltage 1.6130 V 2.0500 V 2.0500 V 2.1900 V
Predicted Resistance 1.1 k 4.7 k 2.0 k 1.5 k
Experimental Resistance 1.0900 k 4.6700 k 1.9800 k 1.4900 k
Predicted Voltage 1.6488 V 2.1028 V 2.1028 V 2.2484
Predicted Current 1.4989 mA .4474 mA 1.0514 mA 1.4989 mA

The team calculated the equivalent resistance with the predicted values and then with the experimental resistances. The predicted Req was 4.0030 k and the experimental Req was 3.9700.

Discussion

The team calculated the experimental error, using the Req’s, and reached the percentage if .82%. The equation for experimental error is; experimental error = (|predicted value - experimental value| / predicted value) 100%. The possible sources of error were machine malfunctions and human error. The machine could not have been hooked up correctly or the equipment could not have been up to date. Human error could include writing the values down wrong or misusing the materials.

Conclusion

The error was a reasonable amount. Since this experiment was discovery driven, there was no need for a hypothesis.
References

1. http://www.corrosion-doctors.org/Biographies/OhmBio.htm
2. http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws