Calculate the percentage difference

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In summary, the conversation discusses a problem with calculating the discrepancy between two calculated values, using equations for finding the difference between values and the error of values. The attempt at a solution involves dividing one value by the other and getting a very large answer, and the potential issue of using different units in the calculations. The conversation also touches on calculating the percentage difference between two values and the importance of using a larger set of measurements for more accurate results.
  • #1
physicsnewby
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Homework Statement


This is related to my last post. Again, I am getting a ridiculous answer hoping someone can help. I need to calculate discrepancy between two calculated values.


Homework Equations



EQN 1 difference between values = Value 2 - Value 1
EQN 2 error of values = square root of (error value 1 ^2 + error value 2 ^2)
discrepancy = EQN 1/EQN2

The Attempt at a Solution


When I use EQN 1, I'm subtracting one value of spring constant k from another. The difference between my values is in the 3000 range. For EQN 2, my error value is in 2 x 10^-3.

When I divide 3000/2x10^-3 I get 1500000 ! The answer should be relatively close to 2!

Now, my previous post was regarding units for k. Could this be the problem? The error values I calculated though were based on the data given in cm, g, seconds squared, etc. Does this matter? It seems strange to me that my calculate K is say 14000.00 +/- 0.003 (for example). Small error for such a large number!
 
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  • #2
Are'nt you suppose to calculate the percentage difference, [tex]p[/tex], between the two values? If the "correct" value is [tex]k_o[/tex] and the experimental value is [tex]k_e[/tex]

[tex]p = 100 \times \frac{|k_o - k_e|}{k_o}[/tex]
 
Last edited:
  • #3
I don't have a correct value to compare to. I have two experimental values I'm comparing.
 
  • #4
Well the formula will give the percentage difference (with the average) if you take half the difference between the two and use the average for the "correct value". It is not really sensible to compare measurements with each other this way though. Statistically one normally calculate the standard deviation and the average of a larger set of measurements.
 
Last edited:
  • #5
Thanks! Figured it out :smile:
 

1. What is the formula for calculating percentage difference?

The formula for calculating percentage difference between two numbers is:
Percentage Difference = ((New Value - Old Value)/Old Value) * 100

2. How do I calculate percentage difference in Excel?

In Excel, you can use the following formula to calculate percentage difference:
=(B2-A2)/A2 * 100, where B2 is the new value and A2 is the old value.

3. What is the purpose of calculating percentage difference?

Calculating percentage difference helps to compare two values and determine the difference between them in terms of percentage. It is often used in statistical analysis and data interpretation.

4. Can percentage difference be negative?

Yes, percentage difference can be negative if the new value is smaller than the old value. This indicates a decrease in the value.

5. How can I use percentage difference in my research?

Percentage difference can be used in research to compare data and determine the significance of any changes. It can also be used to analyze trends and patterns over time.

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