2001/02/08
Christian Habib
Prof. Canning
Phys. NYB


Lab # 1 - Ohm's Law

Introduction

In this laboratory, a multimeter and a computer interface will be used to measure the current in a resistor and the potential difference across the poles of the resistor. When combined, response from the multimeter and the computer is expected to have the form V = RI where R is a constant representing the resistance of the tested resistor (in W) because of Ohm's law. In this case V will represent the potential difference across the resistor (in Volts) and I will represent the current (in mA).

By conducting this experiment we will attempt to verify that the tested resistor obeys Ohm's Law as stated above (V=RI)

The acquired data is plotted in the form of difference of potential vs. current and a curve is then fitted. A direct relationship should then be observed, hence the plot should be of the form y = mx+b where the slope m is the resistance of the tested resistor. Also, y-intercept value b of 0 should be obtained

 


Fig. 1 - Diagram of the circuit used

 

Experimental Results

Voltage (V) Current (mA)
17.4 0.923
32.6 1.738
49.6 2.666
67.4 3.735
85.0 4.570
100.0 5.391
116.4 6.299
134.0 7.276
148.4 8.086

 

Graph

 

Calculations

Result of equation fit: y = .05449212335x - .02540957921

Experimental Error:

Slope:

Y-intercept:

Equation Including Experimental Error:

y = .054492x 0.0016x -.0254 0.10

 

Conclusion

Ohm's Law states that V=RI where V is the difference of potential at the poles of the element (measured in volts), R is the resistance of the element being tested (a resistor in this case, measured in ohms), and I is the current passing through the circuit (measured in milliamps). When the Y-intercept on the attached voltage drop vs. current in the conductor graph is examined, it is observed that the the ranges of R values overlap, also the expected y-intercept value of 0 falls between the maximum and minimum deviation. By further examining the graph,it is possible to notice that the plot of the voltage drop across the conductor versus the current in the conductor results in a straight line. Furthermore, the origin (0,0) is within experimental error for the y-intercept of the graph. Both these statements show that the tested resistor verified Ohm's Law since theoretically the y-intercept should be 0 and the voltage drop across the conductor versus the current in the conductor should be directy proportional. This can be concluded by observing the equation which is y = .054492x 0.0016x -.0254 0.10.

This laboratory had few causes of error that could significantly affect results. The most important factor was a mildly fluctuating power supply (the indicated current did not remain perfectly stable after being adjusted). Another possible cause of error is the possibility of misreading the voltage drop because of the fluctuating power supply. A miscalibrated multimeter could potentially result in inaccurate readings as well since the voltage drop readings were made directly without recalibrating it against a calibrated machine.