816. 1 Coulomb's force law for pointlike charges 4. Coulomb’ s force law ① Experiments: q Q心 (a)Repulse F∝ Q F 1 qe (b)Repulsion F qe Permitivity of free space (c) Attraction E0=8.854187817×10-C/(N·m) @mathematical expression F 4TEor2l 8 16.1 Coulomb's force law for pointlike charges @Compare Coulomb's law and universal gravitational force F 221 F=- r2 For two electrons n grav mCm2=417×10425 §16.1 Coulomb’s force law for pointlike charges 4. Coulomb’s force law 1Experiments: 2 1 r F ∝ 2 r q Q F ∝ 2 0 4 1 r q Q F πε = 8.854187817 10 C /(N m) 12 2 0 = × ⋅ − ε Permitivity of free space q q q Q Q Q 2 21 0 21 ˆ 4 1 r r qQ F πε = r 2mathematical expression 3Compare Coulomb’s law and universal gravitational force §16.1 Coulomb’s force law for pointlike charges 2 21 0 21 ˆ 4 1 r r qQ F πε = r 2 21 21 rˆ r mM F = −G r For two electrons: 2 2 0 elec 4 1 r e F πε = 2 2 grav r m F G e = − 42 2 2 grav 0 elec 4.17 10 4 1 = = × Gme e F F πε