don't know how to read the log chart

Discussion in 'General Electronics Chat' started by sumalama, Nov 20, 2014.

  1. sumalama

    Thread Starter New Member

    Nov 19, 2014
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    Hello,

    can anybody tell me how much value is the red line (point on x axis) is indicating in the figure attached?
    its confusing me.

    thanks
     
    • 5.png
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  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    It looks to me like the line is about half way between  1X10^{^{-4}} and 2X10^{^{-4}} . Since on a log chart, half way is about 3, not 5 (i.e., 10^1/2 =3.16...), I would say the line is 1.3X10^{^{-4}}.

    What is the "correct" answer?

    John
     
  3. sumalama

    Thread Starter New Member

    Nov 19, 2014
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    i thought it was 9.5*10^-3

    so, what is it for sure?
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I thought it was homework. The chart reads left to right, the value has to be less than 10^-3.

    John

    Edit: If you can find an old slide rule at a museum, you can see what I mean.
     
    Last edited: Nov 20, 2014
  5. wayneh

    Expert

    Sep 9, 2010
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    Your's is. One could quibble over the last significant figure, but I agree with your estimate.
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Well, since the mark was in crayon, I didn't try to be too accurate. Besides, it is not often today that you can go back to your old Pickett skills.

    In reality, my intent was to help the TS analyze the question.

    John
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    [​IMG]
    So it is somewhere between 0.0001 and 0.001
    The next mark to the right represents 0.0002
    Hence it is somewhere between 0.0001 and 0.0002

    Now look at a slide rule which uses a log scale:

    [​IMG]

    The cursor is positioned halfway between 0.0001 and 0.0002
    Hence I call it 0.0001414

    Virtual Slide Rule
     
    Last edited: Nov 20, 2014
  8. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I must have been asleep earlier. The range to consider here is not 1 to 10, but rather 1 to 2. I agree the answer is 1.4142... for the half way point.
    John
     
    Last edited: Nov 20, 2014
  9. wayneh

    Expert

    Sep 9, 2010
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    I saw it as not quite halfway, hence 1.3. But upon further review, it is indeed halfway. 1.4 it is.



    Screen Shot 2014-11-20 at 1.52.36 PM.png
     
  10. sumalama

    Thread Starter New Member

    Nov 19, 2014
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    thank guys

    ans = 1.414*10^3
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    That exponent cannot be right based on the image you posted. Is there more to that image?

    John
     
  12. sumalama

    Thread Starter New Member

    Nov 19, 2014
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    oh sorry, i meant

    ans = 1.414*10^4

    no there is nothing more to the image
     
  13. wayneh

    Expert

    Sep 9, 2010
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    Four significant figures? Your eyes must be better than mine. o_O
     
  14. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    The value exactly halfway (as discussed above) between 1 and 2 is 2^1/2 . My earlier error was a brain lapse, and I was considering the range between 1 and 10.

    John
     
  15. wayneh

    Expert

    Sep 9, 2010
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    Yes, but "exactly" is judged by eyeing a crayon mark, and that judgement doesn't warrant 4 sig figs.
     
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