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Homework Help: Ohm's Law and Resistors

  1. Sep 25, 2005 #1
    I know that according to Ohm's Law that the voltage is directly proportional to the current in a resistor. Upon examing my graph that I have calculated in class, a resistor follows Ohm's Law because the slope was a straight line. The part I am confused about is why would the slope be equal to the resistance value? All I can think of is that since the slope increases when the voltage and current increases, then the resistance value increases as well if the resistance value is equal to the voltage/current. Is this correct? Also, would the age of a reisistor have any affect on calculating my data?
  2. jcsd
  3. Sep 25, 2005 #2
    The equation of a line is y = mx, replace y with Voltage, m with Resistance and x with Current and you get Ohm's Law's proportionality, V = IR. I is your independant variable, V your dependant, and R is the proportionality constant, or your slope.
  4. Sep 25, 2005 #3


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    Homework Helper

    the slope of a straight-line graph an any region
    is the rise divided by the run .
    If the line passes through the origin (0,0) , then
    the slope of the line is the SAME all along it.
    (the *line* gets *longer* with more extreme data,
    but does not get *steeper* or shallower)

    If you plotted
    Voltage (vertical axis) vs Current (horizontal axis)
    then the slope is Resistance.
    If you plotted I vs V , the slope is conductance.
    If R increases, then conductance decreases.

    - - - - -
    Resistors age pretty well, unless they're "abused".
    In a college lab-room, abused resistors are common
    unless specifically checked and sorted before lab.
    Usually, "bad" resistors are within a factor of 2
    of what they're supposed to be,
    or else they become infinite or zero resistance.
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