physics p5 help

[desolator619]

can someone PLEASE tell me how to do error bars? or the whole best straight line- worst straight line thing? i've never seen these before and i have no fricken clue how to do them o.o
if someone could help me out or even give me a link to a solved paper 5, i'd be very grateful

 

[desolator619]

59 views and no replies

 

[MW24595]

Hahaha, I'm sorry, shit happens.
Hmm, anyway, it's REAL simple. Chill.

See, you've got your values with their uncertainties, right? The ones in the table.
Well, all you gotta do, is plot in the main point, and then plot the upper and lower limits as well, for that point.
The upper limit is value+ uncertainty and lower limit is value- uncertainty. Obv.
Then, simply connent the 3 dots and draw 2 perpendicular lines at the limits to make them visible.
Voila! It's done.

The best straight line is the line that incorporates the greatest number of points. Or, the line that's closest to all the points. It SHOULD lie within all the error bars.
The worst lines go from the lower limit of the lowest value, to the highest limit of the highest value. And vice versa.
Both worst lines and the best line, all meet at one point.

Hmm, it's simple, all you need to do, is try it out a cuppla times. But it's REALLY time-consuming. :/
As for solved papers, well, the mark schemes all I got, man.
Hope this helps.

 

[desolator619]

how do you get the uncertainty then? like if you look at any of the past papers it's like take value of this and square it and include absolute errors in table and I CAN'T FIGURE OUT HOW TO DO THAT

 

[Swoorup]

After the graph, every uncertainity is calculated from the graph itself.

Gradient uncertainity=G:worst fit- G:best fit
Uncertainity in Y-intercept= Y:worstfit- Y:bestfit

 

[desolator619]

nooo I meant calculating uncertainities in the table. Like suppose you have a table of l/cm and R/ohms and they say "find values of l^2 and include absolute uncertainties in your calculation", how would you do that?

 

[Swoorup]

oh its like this
%uncertainity in l^2=2*%uncertainity in l