lecture 2: electric field, electric field from a point charge, electric field from a dipole

electric field

E = F/q0 with F being the electrostatic force on q0 at the location of q0

• when we want to find the magnitude of the electric field at x, we stick a test charge there, then divide the force on q0 by the charge of q0

electric field lines

electric field lines map out electric field & describe the direction it takes

• electric field lines point towards + and point away from -

• E field is tangent to electric filed lines

what does the density of electric field lines indictae about the electric field?

the greater the density, the greater the magnitude of the electric field at that point

density of field lines = (# of field lines/surface area of sphere)

electric field due to a charged particle

E = (1/4 π ε₀) (q/r²)

electric field from a dipole

E = (1/2 π ε₀) (p/z³)

electric field of a dipole vs. electric field of a single charge

the electric field of a dipole decreases more rapidly with distance than does the electric field of a single charge

• from distant point, a dipole looks like 2 particles that almost — but not quite coincide because they have charges of equal magnitude but opposite signs, their electric fields at distant points almost — but not quite — cancel each other