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Author Topic: error bars physics p5  (Read 1741 times)

Offline winnie101

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error bars physics p5
« on: May 19, 2011, 08:13:12 am »
hey,
can someone help me how to draw the error bars in summer 09 physics paper 5, q 2. ive found the error in the readings, but the errors are so tiny, you cant even see the error bars. or am i doing something really wrong.
Thanks
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Offline winnie101

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Re: error bars physics p5
« Reply #1 on: May 21, 2011, 09:48:41 am »
its may june
Thanks
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Offline aldehyde1612

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Re: error bars physics p5
« Reply #2 on: May 21, 2011, 04:07:43 pm »
I got my error values as : 0.017, 0.012, 0.009, 0.008, 0.007 ... is that what you got?

so the error bars would be a bar from (lgI - error) up to (lgI + error)
Only the last error bar for 0.806 (lgI value) should be very small.. it goes from 0.799 to 0.813.
Make sense??
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Offline winnie101

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Re: error bars physics p5
« Reply #3 on: May 21, 2011, 06:03:13 pm »
oops found my mistake.
Thanks
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Offline winnie101

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Re: error bars physics p5
« Reply #4 on: May 21, 2011, 06:55:55 pm »
another ques,
in may/june 2010 p51 q2 how do i find error in Xc
Thanks
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Offline aldehyde1612

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Re: error bars physics p5
« Reply #5 on: May 22, 2011, 05:03:04 am »
Its the fractional uncertainty in V0 + fractional uncertainty in I0 ...then multiply that by your Xc value.
you add them because to get Xc you divided V/I ... or something along those lines. Maybe try that and see if you get the answer.  :D
« Last Edit: May 22, 2011, 05:04:50 am by aldehyde1612 »
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Offline winnie101

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Re: error bars physics p5
« Reply #6 on: May 22, 2011, 07:18:08 am »
nope, still not working.
this is what is did:
for the first row (0.2/5)+(0.2/0.015)=13.373
then if u multiply this value by value of Xc which is 333, it gives a very large number, 4453.32, whereas the ans is 12
if u could help further id greatly appreciate it
Thanks
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Offline aldehyde1612

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Re: error bars physics p5
« Reply #7 on: May 22, 2011, 11:48:19 am »
Are you sure the answers 12?? .. cause I got 16.7?

where you went wrong is (0.2/0.015)   ..... It should be (0.2/15) cause the x10-3 applies to the error (0.2) as well, so it cancels out when you're dividing.
But with that I get 0.05.. so multiplied by 333 is 16.65? :-\
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Offline TJ-56

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Re: error bars physics p5
« Reply #8 on: May 22, 2011, 02:37:30 pm »
Quote from: aldehyde1612 on May 22, 2011, 11:48:19 am
Are you sure the answers 12?? .. cause I got 16.7?

where you went wrong is (0.2/0.015)   ..... It should be (0.2/15) cause the x10-3 applies to the error (0.2) as well, so it cancels out when you're dividing.
But with that I get 0.05.. so multiplied by 333 is 16.65? :-\

I believe your work is done correctly. The uncertainty for example in the first row = [ (0.2/5) + (0.2/15) ] * 333 ( or 5/15x10^-3 which is 333.33333... ) The answer exactly is 17.77778, which is written simply as 18.
Hope that helped.
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Offline winnie101

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Re: error bars physics p5
« Reply #9 on: May 22, 2011, 04:10:41 pm »
woops, made another mistake reading the marking scheme, u guys are right
Thanks
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