Final answer:
For a good conducting sphere, the electric field within the sphere is zero. For an insulating sphere with uniform volume charge distribution, the electric field inside the sphere is not zero. Therefore, at 4 cm, the electric field from the conductor is zero (EA = 0) and the electric field from the insulator is greater than zero (EB > 0), the answer is 0=EA < EB.
Step-by-step explanation:
When considering two solid spheres with identical charges, the electric field created by them at a certain point depends on whether the sphere is a conductor or an insulator and the location of the point in question relative to the sphere's radius.
For Sphere A, which is a good conductor, all of the charge will reside on the surface of the sphere. According to Gauss's law, within the conducting material and inside the surface of the conductor, the electric field is zero. Since the point at a radius of 4 cm is inside the conducting sphere (radius 5 cm), EA is equal to 0.
For Sphere B, which is an insulator with the charge uniformly distributed throughout its volume, the electric field EB within the sphere is not zero. Instead, it can be calculated using Gauss's law for a sphere with a volume charge distribution, considering only the charge within a Gaussian surface that has the radius of the point of interest (4 cm in this case).
Comparing the two, since EA is zero and EB is greater than zero within the sphere, the answer is 0=EA < EB.