The electric field between infinte plates?

[axcelenator]

Two infinite plates are in the (x,y,z) space. one in X=5 and the second in X=-5. they are charged with superficial density SIGMA. Between them there is a spatial density P. P=A*X^2(X is the variable and A is constant. out the space(for example=X=10 or x=-10) the Electric field is 0.
I have to find the expression for the field(for every x and x) between the plates. How do I do that?
The answer is E=(4/3)(∏)K*A(X^3)

Thanks

 

[Simon Bridge]

Gausses law.

 

[axcelenator]

gauss not works here. if i use it, it gives me ...x^2

 

[cbetanco]

gauss not works here. if i use it, it gives me ...x^2

How do you get $x^2$ when you use Gauss's law? Remember, you have to integrate the charge density. So, what is the integral of $\rho=Ax^2$? Its definitely not proportional to $x^2$.

 

[axcelenator]

thanks! I've figured out my mistake. its fine