IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: winnie101 on May 19, 2011, 08:13:12 am

Title: error bars physics p5
Post by: winnie101 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

Title: Re: error bars physics p5
Post by: winnie101 on May 21, 2011, 09:48:41 am

its may june
Thanks

Title: Re: error bars physics p5
Post by: aldehyde1612 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??

Title: Re: error bars physics p5
Post by: winnie101 on May 21, 2011, 06:03:13 pm

oops found my mistake.
Thanks

Title: Re: error bars physics p5
Post by: winnie101 on May 21, 2011, 06:55:55 pm

another ques,
in may/june 2010 p51 q2 how do i find error in Xc
Thanks

Title: Re: error bars physics p5
Post by: aldehyde1612 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

Title: Re: error bars physics p5
Post by: winnie101 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

Title: Re: error bars physics p5
Post by: 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? :-\

Title: Re: error bars physics p5
Post by: TJ-56 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.

Title: Re: error bars physics p5
Post by: winnie101 on May 22, 2011, 04:10:41 pm

woops, made another mistake reading the marking scheme, u guys are right
Thanks