Am I doing this right?
So the question is in this link down below (Question No. 26)
http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20%289702%29/9702_s08_qp_1.pdf

So here's what I did:

If Intensity is directly proportional to the square of amplitude so that means:

I = A²
I = 8²
= 64

If I = 1/x²
then
64 = 1/x²
x = √1/64
r = 0.125
2r = 0.25

so again if
I = 1/0.25²
I = 16
A = √16
A = 4.0 μm

I think I did it all wrong LOL!!

Question

Am I doing this right?
So the question is in this link down below (Question No. 26)
http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20%289702%29/9702_s08_qp_1.pdf
 
So here's what I did:

If Intensity is directly proportional to the square of amplitude so that means:

I = A²
I = 8²
= 64

If I = 1/x²
then 
64 = 1/x²
x = √1/64
r = 0.125
2r = 0.25

so again if 
I = 1/0.25²
I = 16
A = √16
A = 4.0 μm 

I think I did it all wrong LOL!!