; If the particles can move B they move away from each other

21-4 Coulomb's Law

; If two charged particles B brought near each other B they each exert a force on the other

; If they have the same sing of charge B they repel each other

; If the particles can move B they move away from each other

^.

; If the particles have opposite signs of charge B they attract each other

; If the particles can move B they move closer to each other.

The force of repulsion or attraction B electrostatic force

(21-1)

B

the two particles B has a magnitude of exactly 1 and no

dimension or unit B its purpose is to point r B the distance between them

k B electrostatic constant

along an axis extending through the

masses m _l Û m ₂ B separated by a distance r:

(21-2)

G B the gravitational constant

Both equations B describe inverse square laws B involve a property of the interacting particles B the mass in one case Û the charge in the other

The laws B differ B gravitational forces B always attractive B electrostatic forces B attractive or

repulsive,

This difference B arises from B there is only one kind of mass Û two kinds of charge

^.

Coulomb's law B survived every experimental test B no

exceptions to it have ever been found.

Coulomb's law B holds even within the atom B correctly describing the force B between the positively charged nucleus Û each of the negatively charged electrons.

Coulomb's law B in magnitude form

(21-4)

(21-5) ε ο B permittivity constant Ð

(21-6)

; The gravitational force Û the electrostatic force B both obey the principle of superposition

(21-7)

; shell theorem

A shell of uniform charge B attracts or repels B charged particle B outside the shell as if all the shell's charge B concentrated at its center.

If a charged particle B located inside a shell of uniform

charge B no net electrostatic force B on the particle

Spherical Conductors

If excess charge is placed on a spherical shell that is made of conducting

material, the excess charge spreads uniformly over the (external) surface