% Error

[Lnettie21]

This may sound like a mediocre question but how do you know what the expected values and the experimental values are in an experiment? I am trying to calculate the percent error for an experiment we conducted in lab.

[wolfson]

I am trying to calculate the percent error for an experiment we conducted in lab.

 

Graph ----- Slope ----- Uncertainty and lx values (linest)

 

The graph usually shows uncertainty but you can use formulae to see what an ideal experiment would conclude, but you never get "ideal" you use averages usually.

[aommaster]

As per what I know:

1.Take the amount you of decimal places that you have got.

2. Add another decimal place to that number.

3. Add and subtract on 5 units on that decimal:

 

0.5 ---> 0.50 ---> 0.55 and 0.45

 

4. Find the difference between these two numbers

5. Divide that into the original value, and then multiply by 100 to get teh percentage

 

[wolfson]

Linest is much more accurate.

[Lnettie21]

We did not graph anything. I thought % error= (expected value - experimental value) / expected value.

 

This is the very elementary way of doing it, i just can't remember how to determine what is what.

[wolfson]

To determine Precision you use Standard Deviation, to find the error in an average you use sumx = x1 + x2 + ... + xn, thus x = sumx/n. And there is of course systematic errors, but at your level this is not needed.

[wolfson]

To get a percent it is:

 

Error = experimental value - theoretical value

 

then:

 

Percent error = Error (what you found out above) / theoretical value * 100.

 

And deviation = experimental value - arithmetic mean.

 

Hope that helps.

[Lnettie21]

I understand that but how do you know which is experimental and which is theoretical

[Hades]

experimental is the actual numbers u obtained from performing the experiment; theoretical is the number your experiment has been calculated to be and is the generally accepted numerical value.

 

determining your % error is simple, as wolfson said before.

 

when u have determined your result, and know the theoretical result which should be given to you, then:

 

take your result (experimental) and subtract it from the theoretical.

then take this answer and divide by the theoretical value.

Take this value, and multiply by 100. that is your %.

 

experimental - theoretical

theoretical x 100 %

 

 

 

10 - 10 = 0. 0 / 10 = 0. 0 x 100% = zero.

 

20 - 19 = 1. 1/ 19 = .0526 ....... .0526 x 100% = 5.26%

 

got it?

[Lnettie21]

What does it mean when you get a negative number like -2.28%

[Ms. DNA]

I think you're supposed to use the absolute value of the difference between the theoretical and experimental values, so the negative doesn't mean anything.

[iglak]

yeah, all the negative means is that your experiment results were higher than the theoretical results.

[Hades]

if your experimental results were smaller than your theoretical, then it is negative.

20 - 19 = 1.

18- 19 = -1 -1 / 19 = -5.3%

[Lnettie21]

Thanks everyone

[iglak]

>_<;

oops, you're right