Conductors 10 20 14 9 18 AM Conductors bodies which have a large number of freely moving charges in the electrostatics case For now we will solve after the charges have already settled down and are motionless 1 There can be NO E field inside a conductor o If there is an E field then the electrons will be moving o Charges inside the conductor will produce an E induced which is exactly opposite the E external so the net electric field is zero inside the conductor 2 There can be NO unbalanced charge inside conductors o No charge inside the conductor all the charge goes to the surface o Any introduced induced charge resides on the surface o o 3 Free charge and E fields can exist on the surface of conductors n is the unit vector along the dA vector normal to the surface sigma is the local charge density field must be normal to the surface Example Hollow Conductor with inner and outer surface which has net charge Q Where is charge located in final static situation o No tangential component because it would cause charge flow and the situation has since settled down and is static while the normal component does not cause charge flow Note If you have an infinite disk the electric field is smaller than on a conductor because on a sheet the charge only exists on the surface the equation above is only for infinite sheets Note if sigma is negative that means the electric field points inwards negative charge density Example Find E everywhere for a spherical conductor with charge q Example Find E for an infinite cylindrical conductor with radius a and charge density lambda What happens when you place a conductor in an external field
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