# Physics of a Light Bulb

Physics of a Light Bulb Catherine Bellet Lab Partners: Natalie Russell Alex Harris TA: Chad Lunceford PHY 114 TH @ 2:25pm Abstract: Ohm’s law states, via the equation V=I*R, that the voltage found across a piece of material is proportional to the current. If the temperature remains constant therefore the resistance is found to remain constant. Stefan-Boltzmann law states that when the temperature if above an average of 1000K, then the relationship of voltage and current should be found to be consistent with the formula AT4.

**Physics of a Light Bulb**

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The experimental data found in this, Physics of a Light Bulb, experiment both correlates and verifies the Stefan-Boltzmann law. The voltage and current were found to be proportional to one another, verifying Ohm’s law. In addition, the fact that radiation away from the light bulb is indeed proportional to the fourth power of temperature was observed and again verified through a linear fit graph. The percent error found between the two experimental B values was found to be an average 6%. This showing proving that the experiment was decently accurate.

Objective: To measure the relation between voltage and current in a small flashlight bulb; to determine the temperature of the filament; to verify the Stefan-Boltzmann law of radiation. Procedure: Begin the experiment by correctly setting up the circuit. Using the DMM set, find the resistance of the cold filament of the bulb at room temperature. Open a pre-set experiment file, than connect the circuit to the bulb. Slowly increase the output signal from the power supply, as the voltage reaches 10V, immediately bring the power supply back down to zero.

There should be an observed recorded data and graph in the experimental file. From the recording, highlight the resistance of the cold filament from the data which corresponds to the current ? 0. 08A. Apply a linear fit which in return will give the slope, which represents the bulb resistance. Copy and paste the recorded data into Graphical Analysis, insert various calculated columns, in order to find the temperature of the hot filament and to test the relationship versus power and temperature. Repeat for a second set of data.

Use the graphs to conclude if the Stefan-Boltzmann law is obeyed. Experimental Data: See attached graphs. Results: Resistance of Cold Filament| Experimental Bulb Resistance| % Difference| B1 from Graph1(W/K)| B2 from Graph2(W/K)| % Difference| Theoretical B (W/K)| % Error of B1| % Error of B2| 2. 5? | 2. 46? | 1. 61%| 4. 26| 3. 76| 12. 5%| 4| 6. 19%| 6. 33%| Data Analysis: Discussion: The objective of the lab, Physics of a Light Bulb, was to measure the relationship between voltage and current in a small light bulb, be able to determine the temperature of the filament. nd to verify the Stefan-Boltzmann law of radiation. After completing the lab, the relationship between both the voltage and current was found to be linear, as long as the current is below or at 0. 08 A. This correlation proves Ohm’s law therefore current through a metal conductor is proportional to the applied voltage. Through measurement and observations of the printed graphs, the temperature of the filament of the light bulb was found to be around the value of 1300K.

Using the data supplied from the new calculated columns, the verification of the Stefan-Boltzmann law of radiation was proved to hold true. The law states that when the temperature is above an average value of 1000K, then the relationship between voltage and current is consistent with the formula AT4. When analyzing the curve fit of the power versus temperature graph, it is indeed observed that the experimental value given corresponds with the theoretical function that the power radiated away from the light bulb is surely proportional to the fourth power of temperature.

The percent error observed for both experimental B values, when compared to the theoretical value of 4, shows to be an average of 6%, not a large value of error present. Therefore, the overall system present in the experiment proved to be both precise and accurate. Considering the percent difference between the two experimental resistors was found to be a mere 1. 61%. The percent difference between the two experimental B values was that of a higher value, 12. 5%.

This may indeed have been caused by the fact that the sectioning of data for the second B value was less accurate than that of the first B value. Conclusion: At the conclusion of the experiment, Physics of a Light Bulb, the objective was surely met. The goal was to distinguish the relationship between voltage and current, as well as finding the temperature of the filament, and also to verify the Stefan-Boltzmann law of radiation. Through experimental values, it was observed that the relationship of voltage and current is found to be linear when the current is at or below 0. 8A. The temperature of the filament was also observed to be an average of about 1300K and greater. By taking the values of the Power versus Temperature graph, and creating a new Power versus Temperature raised to the fourth graph and thus applying a linear fit, the relationship of voltage and current was found to be consistent with AT4 and verifying Stefan-Boltzmann law of radiation. Current is indeed proportional to the applied voltage.