Justin Geeslin

Eng Physics II - M 1:00

Experiment Three – Ohm’s Law


  1. Introduction

This experiment exhibits the relationship between current, voltage, and resistance within a controlled circuit. A graph will be used to show the relationship between the three and prove Ohm’s Law. Resistance is defined as potential / current (Volts/ Amps). The resistance will be measure across two different resistors and once across a light bulb.

  1. Procedure

First, on the circuit board, one must connect the power supply to the circuit board for electric current. Then, run lines from the power to one of the resistors. Around the resistor, place the current and voltage probes. With these connections in place, the computer will be able to gauge the amount to voltage and amperage in the system once power is present. First use the 10 Ω resistor. Set the power supply initially to 0 V and zero the probes on the computer. Begin collecting data at 0 V. From here increase the voltage and collect points every 0.5 V until you reach 5 volts. On the graph, the x-axis will be the current, or amperage, as collected by probe 2. The y-axis will be the potential, or voltage. Therefore the resistance will slope of the graph and the y-intercept will be the regression line. Once 5 V is reached and appropriate data is recorded, repeat the process with the 51 Ω resistor.

Next a similar process should be done with the light bulb. Again, initially zero the power supply and computer. Move the wires and probes around the light bulb. In this case, only increase the voltage by 0.1 V for every point. This will reveal the graph as a curve instead of a line. This would infer a varying slope and resistance. Resistance would, in this case, differ because of the change of temperature in the filament. Data should be as follows:

Slope of Regression Line (V/A)

Y-Intercept

10 Ω Resistor

9.863

0.004

51 Ω Resistor

49.82

0.004

Light Bulb (first 3pts)

12.09

0.2453

Light Bulb (last 10pts)

33.05

1.4



Questions

  1. In the resistor graphs, the y-intercept almost exactly zero. The relationship between voltage and current is given by R = V/I.

  2. The resistance as shown by our data table shows the resistance accurately measured up to a 0.2 of an ohm.

  3. The tolerable range for the first resistor would be up to a difference of 1 ohm. Whereas, the second would be up difference of 5 ohms.

  4. Yes, the above data shows the resistance is directly proportional to the voltage and inversely proportional to the current.

  5. In the case of the light bulb, the voltage is increase across the filament allowing the filament the heat up. Although the filament’s brightness does increase with the voltage, it seems to meet a threshold. The filament will only get so bright. This would infer that since the voltage is steadily increasing and the current and resistance must vary with temperature.

  6. Yes, the light bulb still follows Ohm’s law. Only in this case temperature must be taken into account.