ch 5 electric fields L3

electric field is similar to

gravitational; function of space

quantity E can be defined such that

F = QE

whether Q exists or not, E is

a property of space around source charge, whether Q exists or not

electric field of one source charge

E(r) = 1/4πε₀ q/r² * r hat

r hat is

the unit vector pointing away from point charge

direction of E-field is

same as Coulomb force on test charge q, pointing into - and away from +

value of E-field

E = F/Q

far field/electric field of a dipole

E = -1/4πε₀ qd/z³ i hat

when z >> d, decays as

z³ → faster than that of a single charge

electric dipole moment

p such that p = qd, directed from negative charge q to positive charge q

net force on dipole is zero because

positive force + negative force = 0 for dipole inside an external E-field

net torque on dipole is

not zero

induced dipole in atom

external field can polarize an atom - nucleus is pushed along direction of field while electron field is pushed oppositely

how to deal with extended charges

divide into infinitely small chunks, each is a point charge; E_p = 1/4πε₀ ∫ dq/r² * r hat