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Homework Help: Meter Bridge.

  1. Mar 26, 2016 #1
    1. The problem statement, all variables and given/known data
    Q0lRdWc.png

    2. Relevant equations
    How to find error in resistance ?

    3. The attempt at a solution
    I found out the resistance without error.
    But What is the way to figure out an error of an instrument ?
     
  2. jcsd
  3. Mar 26, 2016 #2

    ehild

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    Write the formula you use to calculate the unknown resistance. You read the position x of the slide contact with error of dx= 0.1 cm (or 0.05 cm). R is a function of x: R=f(x) and its error is dR=f ' (x) dx.
    Some people consider the reading error as the smallest scale, other consider half of it as the reading error.
    If you do not want to differentiate, calculate the resistance with the reading changed by ± the reading error. If it is ±1 mm, calculate the resistances with x=36.1cm and 35.9 cm, and give the deviation from the resistance calculated with x=36 cm.
     
  4. Mar 26, 2016 #3
    As per your given hint,
    i calculated resistance.
    When x=36.1 cm , R=9.03 ohm
    When x=35.9 cm, R=8.96 ohm

    What does that mean ?
     
  5. Mar 26, 2016 #4

    ehild

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    You got 9 ohm with x=36. So the reading error makes the resistance value deviate about 0.3-04 ohm from the real one. To which answers is it closest?
    I suggest to apply the other method, taking the derivative of R=f(x) and multiplying it with the reading error.
     
  6. Mar 27, 2016 #5
    T5OhaS2.png
    Right ?
     
  7. Mar 27, 2016 #6

    ehild

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    If l is the length read on the meter, it is right. Take the derivative with respect to l at l=36 cm and multiplied it with Δl=0.1.
    It is possible that the error of the reading is considered half of that, then the error of the resistance is also halved.
     
  8. Mar 27, 2016 #7
    I got it now !
    Thanks for your help @ehild :wink:
     
  9. Mar 27, 2016 #8

    ehild

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    You are welcome.
     
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