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Proving an exponential relationship

Physics A2
I know how to prove that something is exponential with regards to time (graph of natural log whatever against time gives a negative gradient with +ve y intercept. I have only ever seen these exponential relationships with time and the notes my teacher gave just say "to prove something is exponential take logs of values". If time is not a variable do you still end up with a graph of natural log whatever against the other variable or do you take logs of both variables?

Thank you!
Reply 1
Original post by Orangemonkey1
If time is not a variable do you still end up with a graph of natural log whatever against the other variable


Yes, you do.
Original post by Zacken
Yes, you do.


Thank you!
Reply 3
Original post by Orangemonkey1
Thank you!


No problem! I've moved this to the Physics forum for you; in the future, try and post physics related question here. You'll get more attention quicker! :biggrin:
Original post by Orangemonkey1
Physics A2
I know how to prove that something is exponential with regards to time (graph of natural log whatever against time gives a negative gradient with +ve y intercept. I have only ever seen these exponential relationships with time and the notes my teacher gave just say "to prove something is exponential take logs of values". If time is not a variable do you still end up with a graph of natural log whatever against the other variable or do you take logs of both variables?

Thank you!

Just be careful because that negative part proves exponential decay. The gradient could be positive if it were an exponential growth (e.g. in a capacitor charging up)

Also as a quick tip, remember that in physics, the units for log(dimension) are the same as the units of the actual dimension. I know it seems weird but for example ln(time), where time is measured in seconds, would still be measured in seconds. You must remember this when labelling graphs!
Reply 5
Original post by Student403
Just be careful because that negative part proves exponential decay. The gradient could be positive if it were an exponential growth (e.g. in a capacitor charging up)

Also as a quick tip, remember that in physics, the units for log(dimension) are the same as the units of the actual dimension. I know it seems weird but for example ln(time), where time is measured in seconds, would still be measured in seconds. You must remember this when labelling graphs!


So it's not In(seconds) ???
Original post by Kyx
So it's not In(seconds) ???


Nope.

Unit is seconds
Reply 7
Original post by Student403
Nope.

Unit is seconds


Why?

I mean, time^2 is measured in seconds^2 ... ???
Original post by Kyx
Why?

I mean, time^2 is measured in seconds^2 ... ???


Yes because that's [time] * [time]. Ln is a function
Reply 9
Original post by Student403
Yes because that's [time] * [time]. Ln is a function


Oh

and is it L n or I n?

y'know as in 'in'

do you say 'in 3'???
Original post by Kyx
Oh

and is it L n or I n?

y'know as in 'in'

do you say 'in 3'???


Lower case L.

Can be pronounced "lun" or "L.N.", however you want to.
Reply 11
Original post by Student403
Lower case L.

Can be pronounced "lun" or "L.N.", however you want to.


So when I wrote 'in' on my ISA, I am going to lose a mark?
Original post by Kyx
So when I wrote 'in' on my ISA, I am going to lose a mark?


you dotted your i?
Reply 13
Original post by Student403
you dotted your i?


No, I did capital I withn lines at the top and bottom
Original post by Kyx
No, I did capital I withn lines at the top and bottom


That'll be fine. It's how some people draw their lower case Ls anyway

Spoiler

Reply 15
Original post by Student403
That'll be fine. It's how some people draw their lower case Ls anyway

Spoiler



:smile:

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