In the last page of notes, we talked about two different examples of distributions of charges (both spheres and cylinders) for both conducting materials and insulating materials. It is worth highlighting some common features and patterns of fields for these larger shapes.

• Electric field should point radially away (for a positive charge) or toward (for a negative charge) a sphere
• Electric field should point radially away (for a positive charge) or toward (for a negative charge) a cylinder - except near the ends

• If you are looking for the electric field outside the object with a simple shape (sphere, cylinder), it doesn't matter if it is an insulator or conductor - the electric field will be the same (for the same amount of charge uniformly distributed).
• If you are looking for the electric field inside a conductor, it will always be zero (no matter what the shape).
• If you are looking for the electric field inside an insulator, it will likely be non-zero (expect perhaps in the very center for certain cases).

• Charges move to the surface of conductors - there is not net charge inside the conductor (the atoms are still there, but they are neutral).
• Charges stay where they are placed on insulators - it is possible to have net charge in inside an insulator.

• If you are looking for the field outside of a sphere with a uniform distribution of charge, we will often approximate the sphere as a point charge because the electric field is the same for both of these cases.
• If you are looking for the field outside of a cylinder with a uniform distribution of charge, we will often to approximate the cylinder as a line of charge because the electric field is the same for both of these cases.