# Thread: Using Graphical Techniques to find values

1. ## 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

2. ## Re: Using Graphical Techniques to find values

Starting with your equation $\displaystyle I=aV^n$

Take the log of both sides

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

Sort out the right hand side a bit

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

and a bit more

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

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

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

Are you OK from there?

3. ## Re: Using Graphical Techniques to find values

Thank you very much, thats a great help. I shall give it a go.

4. ## 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.