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Percentage uncertatainty

  • Thread starter moimoi24
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  • #1
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Homework Statement



In a simple electrical circuit, the current in a resistor is measured as 2.5 ± 0.05 mA. The resistor is marked as having a value of 4.7 Ω ± 2%. If these values were used to calculate the power dissipated in the resistor, what would be the percentage uncertainty in the value obtained?

Homework Equations



none

The Attempt at a Solution


please help me, what is the solution for this one? thanks

i'm sorry, i post this in the advanced physics too, i'm confused where to post this.. hope you can help me...
 

Answers and Replies

  • #2
PeterO
Homework Helper
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Homework Statement



In a simple electrical circuit, the current in a resistor is measured as 2.5 ± 0.05 mA. The resistor is marked as having a value of 4.7 Ω ± 2%. If these values were used to calculate the power dissipated in the resistor, what would be the percentage uncertainty in the value obtained?

Homework Equations



none

The Attempt at a Solution


please help me, what is the solution for this one? thanks

i'm sorry, i post this in the advanced physics too, i'm confused where to post this.. hope you can help me...
I think that when multiplying two quantities, you merely add the percentage errors??

In this case you are multiplying 3 things I x I x R as in P = I2R; so you would add all three percentage errors.
You are given the percentage error in R, and can calculate the percentage error in I from the values given.

Peter
 
  • #3
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Can you show me the solution? i'm confused... thanks peter...
 
  • #4
PeterO
Homework Helper
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Can you show me the solution? i'm confused... thanks peter...
If you wish to calculate the area of a rectangle with length 5.0 ±0.1 cm by 10.0 ± 0.1 cm, and give a percentage uncertainty, then

A = l x w so Area = 50 cm2

Now the percentage error.
5.0 ± 0.1 means an uncertainty of 0.1 in 5 or 1 in 50 or 2%
10.0 ± 0.1 mans an uncertainty of 1 in 100 or 1%

SO the uncertainty in the answer is 3% [add them together]

So Area is 50 cm2 ± 3%

That is as close to the solution you seek I will give,
 

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