2001/02/08

Christian Habib

Prof. Canning

Phys. NYB

Lab # 1 - Ohm's Law

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

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 |

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

Slope:

Y-intercept:

y = .054492x ± 0.0016x -.0254 ± 0.10

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.