Chapter 26 Electric Potential 第二十六章 電位

Lightning

Just before lightning

Electric potential energy

Electric potential energy where W is the work done by the static electric field. For convenience we often define Where is the work done by the field to move the charge particle from infinity to its current position and .

Electric potential In general we have

Work done by an applied force If ΔK = 0, then

Equipotential surfaces Surfaces in space on which V is constant.

Equipotential surfaces If ΔV is chosen to be the same for all adjacent equipotential surfaces, then the electric filed is inversely proportional to the separations of the equipotential surfaces.

Calculating the potential from the field or Vi can be assigned to any convenient value such as 0.

Potential due to a point charge If

Potential due to a point charge

Potential due to an electric dipole If the point of interest P is far away from the dipole, then

Potential due to an electric dipole

Induced dipole moment

Potential due to a group of point charges Example

Potential due to continuous charge distribution

Line of charge

Charged disk

Calculating the field from the potential

Electric potential energy of a system of point charges

Potential of a charged isolated conductor

Surface charge density of a conductor

Electric fields near a conductor The field strength is strongest at the point on a conductor where its local curvature of radius is the smallest.

Image charge

Home work Question (問題): 8, 15, 21 Exercise (練習題): 5, 12, 19 Problem (習題): 12, 28, 29, 37