# Testing for an exponential relationship?!!

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#1
I have had this question come up millions of times on my physics papers and i still cant do it!!
I mean the situation where they either give u values or a graph and you have to test if the relationship is exponential.
Can somebody pleaseeeeeeee explain to me how to do it, ill give rep as a bribe because i have such a mental block !!!
Please make it not too maths-y lol, im mathematically challenged, i just need to know the basic way to calculate this :P

0
13 years ago
#2
don't you just draw lines on the graph to show a constant half life?
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13 years ago
#3
With values, try a logarithmic curve, if straight line then exponential relationship.
0
13 years ago
#4
Say you want to test exponential relationship between A and B:

test A = k e^B which is an exponential relationship, where k is a constant

so

lnA = lnk + B (learn your exponential laws!)

Plot lnA against B - if straight line, then exponential relationship is established.
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#5
ok so say you had to work out the realtionship without drawing a graph, just using values FROM an already plotted graph.. does it work the same way?
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13 years ago
#6
(Original post by little_em)
ok so say you had to work out the realtionship without drawing a graph, just using values FROM an already plotted graph.. does it work the same way?
Yes.
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6 years ago
#7
Don't know if this thread is still live, but if anyone checks by then the method I prefer is testing for a common ration.

say you have your data in some kind of table. if the relationship is exponential, then dividing each entry in the F(x) (dependent variable) column by its immediate neighbour above or below should give pretty close to the same value. Just make sure you're consistent with which neighbour you choose (above or below).

Hope this helps someone, somewhere, somewhen.
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