Using Graphical Techniques to find values

• Apr 14th 2012, 08:03 AM
MrMagoo
Using Graphical Techniques to find values
Hi there,

was looking for some advice and assistance on a particular question if at all possible. I'm looking to solve the following:

results were collected in an experiment to find the relationship between the luminosity (I) of a lamp and the voltage (V). The law is thought to be of the type I=aVn

Now I need to plot Log I (Vertically) against Log V (Horizontally) and find the values of A and N. The data is below.

V 40 60 80 100 120

I 5.1 26.0 82 200 414

Any tips on how I go about solving this will be greatly appreciated.

Thanks
MrMagoo
• Apr 14th 2012, 09:20 AM
a tutor
Re: Using Graphical Techniques to find values
Starting with your equation $I=aV^n$

Take the log of both sides

$\log I=\log(aV^n)$

Sort out the right hand side a bit

$\log I=\log(a)+\log(V^n)$

and a bit more

$\log I=\log(a)+n\log(V)$

$\log I=n\log(V)+\log(a)$

You've now got it in the form $Y=mX+c$.

Are you OK from there?
• Apr 15th 2012, 03:22 PM
MrMagoo
Re: Using Graphical Techniques to find values
Thank you very much, thats a great help. I shall give it a go.
• Apr 16th 2012, 12:20 PM
MrMagoo
Re: Using Graphical Techniques to find values
Would anyone be able to advise me with what I need to do with the log functions?

now its in the form of y=mx+c I assume I create my graph with the results obtained and then use this to find the values of m and c which equate to a and n.

In summary do the log functions change anything and if they do in what way.

Many thanks for any help received.