18.4.1—E = Q / (4πε0 r 2) for the electric field strength due to a point charge in

The field magnitude due to point charge Q at distance r is E=|Q|/(4πε₀r²), directed away from positive Q and toward negative Q.

The field is a property of the source, independent of the test charge used to measure it. Add fields as vectors for several sources.

At twice the distance from a point charge, field strength is one quarter as large.

E is not the force on every charge; the force is qE and depends on the test charge.