• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

Physics: Post your doubts here!

X

xyz!

Messages
99
Reaction score
27
Points
28
rheea.cool said:
can you tell me how to find absolute uncertainity anyone?
Click to expand...
hi sum1 had posted dis in sum other thread..i m pasting it here for u..c if it helps!
Example: Find lg R and its error and record in the table

R =231 +/- 10 (3s.f)
lg R should be to 3 sf

lg 231 = 7.85174904142
=> lg 231 = 7.852 (to 3 sf)

Notice in lg 7.852 is to 3 s.f and not 4. The numbers before the . do not count
E.g :
0.039 = 3 sf
3.430 = 3sf
3.4503 = 4sf
0.0002 = 4sf

Now the error in lg R = |lg Rmax - lg R|
Rmax = 231+10 = 241
Lg Rmax = Lg(241) = 7.91288933623 = 7.913 (to 3sf)

Therefore error in Lg R = |lg Rmax - lg R| = |7.913 - 7.852| = 0.061

So you record Lg R in the table as follows: 7.852 +/- 0.061

As you will see error above is to 3 s.f. Exceptionally in P5, the errors IN THE TABLE can be to more than 1s.f.

However when you will be calculating gradient and y-intercepts, you should bring the the error to 1s.f
Example for final answers of gradient and y-intercept:
gradient = 5.02 +/- 0.03 << Error to 1 s.f
y-intercept = 1.20 +/- 0.01 << Error to 1 s.f

So if it happens when u calculate gradient u get:
5.321 +/- 0.324 << This answer is not good and won't be accepted. You should work out the answer to the correct SF for the error. So you proceed as follows:

=>5.321 +/- 0.324 , error should be to 1 sf
=> 5.321 +/- 0.3 , now error in to 1 sf, but the gradient value is not good. Error is 1 SF but 1 D.P, so gradient should be to 1 D.P
=> 5.3 +/- 0.3 <<<<< That's the final answer for gradient


So to summarise:
> error in calculated values IN TABLE can exceptionally be to more than 1 sf.
> error in final answers for gradient or y-intercept should IMPERATIVELY be to 1 sf. Then you proceed as I explained above to get the final answer.


I suggest you go and work Nov 2009 P51. You will understand everything based on that paper. It's really the paper which has the most difficult data I've ever encountered.
 
You must log in or register to reply here.
Top