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Electrical/Math hw question

  1. Sep 1, 2006 #1
    Hey! I'm not sure where this goes but it has to do more with math than electrical. To start things off, we were given Voltage (10v) and a resistor source (100ohms). This had to be done in excel, where we would enter the formula for 11 values and excel would calculate the answers. Then we graph Current and Load voltage, ect. This is what I got, http://img515.imageshack.us/img515/7241/untitledjb8.jpg

    Heres the question: Where does the plot intersect the vertical axis? If extended, where would it intersect, the horitzontal axis?

    Either I'm making to much of this question or I did something wrong. Now, I know the vertical axis goes up and down (Y) and the horitzontal axis goes from left to right (x). So basically, it touches 40-100 and 0-6?

    Thanks for any help.
    Last edited: Sep 1, 2006
  2. jcsd
  3. Sep 1, 2006 #2


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    Staff: Mentor

    The y intercept is the "short circuit current" where there is no voltage across the short circuit. It's where that line intersects the y axis at x=0 (zero volts). What is that current?

    The x intercept is the "open circuit voltage". That's where there is no output current (so y=0). What is the voltage where the line finally gets down to the y=0 level?
  4. Sep 1, 2006 #3


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    Is this for a math or electronics class? Are you measuring current for a given voltage?

    If you do not know about electronics; based on your plotted points you could make a reasonable guess, that the relationship between voltage and current is linear.

    Recall from algebra, you can predict the x and y intercepts, given points on a line. But if these are measured data, this line may not be exactly linear. So some simple statistics may be done to calculate the slope of your data. In Excel you could find the SLOPE and INTERCEPT (y-intercept) using the Functions on your data set. Now, if you recall the algebraic equation for a line, you can then find your x-intercept.
    Last edited: Sep 1, 2006
  5. Sep 3, 2006 #4


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    How did you make out finding the x and y intercepts of your data?

    if there is anything you don't understand about our suggestions, please ask more questions! :smile: we can help steer you towards a successful solution.
  6. Sep 4, 2006 #5
    No, thanks, I got it now. Sry, I didn't have time to post. Berkeman hit the spot. :)

    This is actually for computer class. We are learning how to use excel by using formulas and such. These were questions to think about. Thanks for the help.
  7. Sep 4, 2006 #6


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    In The Excel chart menu is a option for trendline, this will generate a best fit line to your data, you can display the equation of the line on your chart, and even choose to extend your line to points you enter. Very much easier then using the Excell LINEST function which requires defining an array.
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