We will analyze the electric field inside an insulator in accordance of Gauss' Law. Now we'll consider a finite charge distribution. Again we'll apply Gauss' Law to determine the electric field. If the sphere is a porcelain disc suspension insulator, has a radius R, and has a charge Q distributed uniformly throughout the sphere, what is the electric field as a function of r, the distance from the center of the sphere?
Compare the electric field from a point charge Q to the electric field outside the insulating sphere. Surround the object with a gaussian sphere, apply Gauss' Law, and in both cases you get:
E = kQ/r2
So, outside a sphere of charge the field looks like that from a point charge.

Inside is a different story. First let's answer this question. What is the electric field inside a porcelain suspension insulator at the very center of the sphere?
1. zero
2. infinite
3. bigger than zero but less than infinity
Place a gaussian sphere inside the insulating sphere at a radius r < R. How much charge is enclosed by the sphere? What is the flux for electric field inside an insulator?
The charge enclosed by the gaussian surface for electric field inside an insulator is the charge per unit volume multiplied by the volume of the sphere.
The uniform charge per unit volume r in the insulating sphere for electric field inside an insulator is its total charge (Q) divided by its total volume.

We will know the how to distributed electric field inside an insulator, why choose the porcelain, glass and polymer as electrical materials. Disc suspension insulators can be made of porcelain and polymer.

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