Lnettie21 Posted March 31, 2004 Share Posted March 31, 2004 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. Link to comment Share on other sites More sharing options...
wolfson Posted March 31, 2004 Share Posted March 31, 2004 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. Link to comment Share on other sites More sharing options...
aommaster Posted March 31, 2004 Share Posted March 31, 2004 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 Link to comment Share on other sites More sharing options...
wolfson Posted March 31, 2004 Share Posted March 31, 2004 Linest is much more accurate. Link to comment Share on other sites More sharing options...
Lnettie21 Posted March 31, 2004 Author Share Posted March 31, 2004 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. Link to comment Share on other sites More sharing options...
wolfson Posted March 31, 2004 Share Posted March 31, 2004 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. Link to comment Share on other sites More sharing options...
wolfson Posted March 31, 2004 Share Posted March 31, 2004 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. Link to comment Share on other sites More sharing options...
Lnettie21 Posted March 31, 2004 Author Share Posted March 31, 2004 I understand that but how do you know which is experimental and which is theoretical Link to comment Share on other sites More sharing options...
Hades Posted March 31, 2004 Share Posted March 31, 2004 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? 1 Link to comment Share on other sites More sharing options...
Lnettie21 Posted March 31, 2004 Author Share Posted March 31, 2004 What does it mean when you get a negative number like -2.28% Link to comment Share on other sites More sharing options...
Ms. DNA Posted March 31, 2004 Share Posted March 31, 2004 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. Link to comment Share on other sites More sharing options...
iglak Posted April 1, 2004 Share Posted April 1, 2004 yeah, all the negative means is that your experiment results were higher than the theoretical results. Link to comment Share on other sites More sharing options...
Hades Posted April 1, 2004 Share Posted April 1, 2004 if your experimental results were smaller than your theoretical, then it is negative. 20 - 19 = 1. 18- 19 = -1 -1 / 19 = -5.3% Link to comment Share on other sites More sharing options...
Lnettie21 Posted April 1, 2004 Author Share Posted April 1, 2004 Thanks everyone Link to comment Share on other sites More sharing options...
iglak Posted April 2, 2004 Share Posted April 2, 2004 >_<; oops, you're right Link to comment Share on other sites More sharing options...
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