Question on electric filed of an insulating cylinder

[loba333]

An infinitely long insulating solid cylinder of radius R contains a non-uniform
spherically symmetric charge distribution, whose density is given by
rho r = rho(0) r/ R. Calculate the electric field a distance r from its axis:
(i) when r > R;
(ii) when r < R.

Can some please expalin to me how to do this. i could be able to do it for a sphere with a charge q but the formula (rho r = r(0) r/ R) has thrown me off.

Heres the question
http://i1200.photobucket.com/albums/bb327/loba333/photobucket2.png

Cheers guys !

 

[loba333]

Why is there an r either side of the quation ?

 

[gomunkul51]

loba333 probably meant rho(r) = (rho(0)/R)r, as in rho a linear function of r.

 

[loba333]

Can you guys please helo me iv attempted the solution but i don't know if its right:
http://i1200.photobucket.com/albums/bb327/loba333/IMG_1461.jpg

 

[loba333]

no one ?

 

[gneill]

The problem states that the cylinder is insulating, with a given charge distribution throughout. So for iii) your assumption about the enclosed charge being zero for r < R is invalid.

You're going to want to find expressions for the total charge contained within the Gaussian surface per length L, then apply Gauss' law to find the form of the electric field.