IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: Gaz on June 08, 2010, 04:49:14 pm
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Usually the 2nd question requires drawing a graph with a line of best and worst fit. Is the error in the gradient of the line of best fit calculated by (gradient of best-fit line – gradient of worst acceptable line)?
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yep.
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quick question:
which of these is considered the line of best fit?
this
http://i45.tinypic.com/29ys9c3.png
or this
http://i46.tinypic.com/k0od9d.png
??
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quick question:
which of these is considered the line of best fit?
this
http://i45.tinypic.com/29ys9c3.png
or this
http://i46.tinypic.com/k0od9d.png
??
i believe it is the 2nd one:
http://i46.tinypic.com/k0od9d.png
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i believe it is the 2nd one:
http://i46.tinypic.com/k0od9d.png
i know it LOOKS right but the first one passes through more points :-\
and what exactly IS the line of best fit? isn't it the line that passes through the most points?
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Yup. I too am not sure of the definition of a line of best fit. Use this:
http://staff.argyll.epsb.ca/jreed/math9/strand4/scatterPlot.htm
It might help in understanding the line of best fit.
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True. Your first passes through more points but that's not the line of best fit for sure as 2 points are above the lines =)
For a line to be a best fit - it must passes through most points (though not necessarily) or most points must lie evenly along the line. For e.g. you can't have 2 points above the line (as in your first line) and none below. If 3 points are above the line, there should also be 3 points below - hence, evenly spread.
Hope it make sense =]
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I just checked. Your right. There has to be just as many points above the line as below. One either way if the number of points are odd.
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hmm alright, thanks
i have another question.. in nov 09 the second variant, question 2 part d
to calculate the uncertainty i multiplied the percentage error in the gradient by the value i got for g, and i got 1.5
in the mark scheme it says to subtract the g you get from the gradient - g from worst acceptable line.. if i do that, i get 1.2
is my way also correct?
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quick question:
which of these is considered the line of best fit?
this
http://i45.tinypic.com/29ys9c3.png
or this
http://i46.tinypic.com/k0od9d.png
??
the 2nd one is the line of best fit
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one more question ,
How do we calculate absolute errors in the values of l^2??
the paper is attached, Q2 (b)
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one more question ,
How do we calculate absolute errors in the values of l^2??
the paper is attached, Q2 (b)
percentage error in l^2 = percentage error in l X 2
multiply that by whatever value you get for l^2
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in nov 09 the second variant, question 2 part d
to calculate the uncertainty i multiplied the percentage error in the gradient by the value i got for g, and i got 1.5
in the mark scheme it says to subtract the g you get from the gradient - g from worst acceptable line.. if i do that, i get 1.2
is my way also correct?
anyone? :(
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anyone? :(
Hmm. But personally i think the whole point of drawing a worst acceptable line is to calculate errors so yeah. Stick to the mark scheme method.
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this might help some one
http://www.mediafire.com/?sharekey=17ec329bec83263bdc09e7d393492eee47b0d1e1ae287e254ad239450a8c1cf1
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how to find the error in gradient if the slope is negative? Let say the best fit gradient is -0.017 and worst fit line is -0.024, i am just plucking two value randomly, but the main concern is the negative. How to find uh?? is it like -0.017- (-0.024) which make the - and - become +..Is that a right way??
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I think you just find the difference between the two
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Find the difference between best and worst fit and divide by 2
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Find the difference between best and worst fit and divide by 2
you don't divide by two...?
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I just said divide by 2.
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DONT divide by 2
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Divide by 2 if you have lines of worst and biggest fit.
Dont divide by 2 if you have line of best and worst, or best and biggest.
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Divide by 2 if you have lines of worst and biggest fit.
Dont divide by 2 if you have line of best and worst, or best and biggest.
where'd you get that from? :-\
you only divide by two if you use the gradients of the SHALLOWEST and STEEPEST worst acceptable lines.
if you're using the line of best fit with either one of the worst acceptable lines, you don't divide by two.
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@falafail-that was what i was trying to say-lol.