Understanding Absolute Error & Resistance of Wires

[khizman]

Anyone can explain to me what Absoloute Error is and what this means:

Worst case % error = Absolote error/ Smallest reading * 100

For Voltmetre ______ %
For Ammetere ______ %
For Length _______ %
For Diametre _______%
_________________
Overall % error __________%

this if for a project on resistance of wires. 3 parts length, thickness, type of material.

heres a screenie of a sample of my reuslts
http://img439.imageshack.us/img439/9977/screenei4xw.jpg


Thanks For any help in advance

 

[Chi Meson]

Worst case % error = Absolote error/ Smallest reading * 100

I have never heard of "worst case error." But anyway...

Error is stated in two ways: relative error and absolute error.

The relative error is the percentage form such as " 20 meters plus or minus 5%"

The absolute error is in the unit of measurement, indicating the uncertainty of the final digit, such as "20 meters plus or minus 1 meter"

Notice in both cases the error is the same. When adding or subtracting quantities, you must add the absolute error. When multiplying or dividing quantites, you add the releative error.

 

[khizman]

this plus or minus, in my case i don't have any plus or minus i don't think?

I know that my crocodile clip was 2 mm so that must affect my length measurement in some way/

 

[Chi Meson]

the plus or minus is the uncertainly of the measurement. If your alligator clip made your measurement uncertain by 2 mm, so that your measurement is "between 23 and 25 mm," then the measurement is :
24 mm plus or minus 1 mm. (relative error) or
24 mm plus or minus 4% .

 

[khizman]

hmm so that mean when i meaure my length of 5 cm (50mm) it could be plus or minus 4% is that corect?

 

[Hootenanny]

hmm so that mean when i meaure my length of 5 cm (50mm) it could be plus or minus 4% is that corect?

No because your croc clip was always 2mm its length is not affected by an increased length of wire, you need to use the absolute error. Therefore, your measurements will always be $X mm \;\; \pm 2mm$. Do you follow?

-Hoot

 

[khizman]

but say i measure 5 cm isn't my crocodile clip affecting that length by 2mm
plus or minus?

 

[Chi Meson]

2 mm is 4% of 50 mm, so it would be
50 mm +/- 4% [latex isn't working for me: "+/-" means "plus or minus"]
2mm is 3% of 66mm, so that would be
66 mm +/-3%

both have the same absolute error, but different relative errors.

 

[khizman]

so to work this formula out of,

worst case % error = absoloute error (is that 4% or +/- 2mm?) / smallest reading ( 5cm? ) *100

 

[Hootenanny]

Worst case;

$$=\pm \frac{2\times 10^{-3}}{0.05} \times 100$$

Regards,
~Hoot