Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need confirmation on lightbulb experiment

  1. Oct 2, 2012 #1
    I was piddling with my meter and graphing calculator and came up with this equation

    y= .08x+.14

    This equation uses the number of batteries for X, and the Amp draw through a light bulb for Y.

    The results are theoretical past 4 batteries.

    The batteries were 1.29 v when the experiment began.

    The real question here is about resistance.

    Outside here it is about 80 degrees F, the ohmmeter showed 1.3 ohms from the light-bulb. The light bulb, using Ohms law, will have a resistance of ~11.4667 ohms when ~5.16 V are put to it. Meaning an amp draw of ~.45A

    *With this initial resistance and final resistance being known, can I use a linear model to find the resistance of the bulb for each individual cell?*

    How would this model be constructed?

    If a graph were to be constructed it would start at (0,1.3) and end at (4, 11.46667). Is there any digital way of finding the missing values?

    Kind of a math question isn't it?
    Last edited: Oct 2, 2012
  2. jcsd
  3. Oct 3, 2012 #2


    User Avatar

    See part 2 in this link. It describes exactly your experiment, even uses your method of force voltage with batteries, and how to plot out the v vs i curve and what not.

    http://teachers.usd497.org/agleue/unit_pdfs/electricity_unit_1/electricity_unit_1_ohm_laws_and_light_bulb_lab.pdf [Broken]
    Last edited by a moderator: May 6, 2017
  4. Oct 3, 2012 #3


    User Avatar

    btw, i found this via a google when looking for the v vs i of a light bulb over this voltage range. here the bulb's large signal behavior isn't ohmic so it can't be modeled accurately over this range with an equation of the form y=mx+b.

    you'll see all that, and an explanation, in the results section of the link above.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook