UNIVERSITY PHYSICS II CHAPTER 16 Forces and lectric Fields 8 16.1 Coulomb's force law for pointlike charges 1. The discovery of electrification OThe phenomenon of electrification Glass rod is rubbed with silk--positive Amber rod is rubbed with fur --negative ② electric charge is an intrinsic characteristic of the fundamental particles making up Neutral copper matters Charged plastic
1 1. The discovery of electrification 2electric charge is an intrinsic characteristic of the fundamental particles making up matters. 1The phenomenon of electrification Glass rod is rubbed with silk—positive Amber rod is rubbed with fur--negative §16.1 Coulomb’s force law for pointlike charges
816. 1 Coulomb's force law for pointlike charges Glass Plastic @like charges(charges with the same sign) repel each other and unlike charges(charges with opposite electrical signs)attract each other 8 16.1 Coulomb's force law for pointlike charges 2. The properties of electric charge Othe charges are scalar: @charges are quantization; e=1602177*10-1CgF=ne up quarks: 2e/3, down quarks: -e/3 Othe total amount of electric charges is conserved in any process involving an isolated system 3. The polarization and induction Why can comb rubbed with fur attract small pieces of paper?
2 3like charges(charges with the same sign) repel each other, and unlike charges(charges with opposite electrical signs) attract each other. §16.1 Coulomb’s force law for pointlike charges §16.1 Coulomb’s force law for pointlike charges 2. The properties of electric charge 1the charges are scalar; 2charges are quantization; e=1.602177*10-19C q=ne up quarks: 2e/3, down quarks: -e/3 3the total amount of electric charges is conserved in any process involving an isolated system. 3. The polarization and induction Why can comb rubbed with fur attract small pieces of paper?
816. 1 Coulomb's force law for pointlike charges 8 16.1 Coulomb's force law for pointlike charges insulator Electric dipole electrical polarization conductor induction grounding
3 §16.1 Coulomb’s force law for pointlike charges §16.1 Coulomb’s force law for pointlike charges + + + + + −−− − − − − −− − − + + +++ + ++ + + + −− − − − − − −− − − induction + + + + + grounding conductor induction + + +++ + electrical polarization insulator − + − + − + − + − + − + − + Electric dipole
816. 1 Coulomb's force law for pointlike charges 8 16.1 Coulomb's force law for pointlike charges A
4 §16.1 Coulomb’s force law for pointlike charges §16.1 Coulomb’s force law for pointlike charges
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=417×1042
5 §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