电场（PPT课件讲稿）Electric field

Chap 22-24 Electric field First circular accelerator in the world

First circular accelerator in the world Chap 22-24 Electric field

Easy chair Charged hair

Easy chair Charged hair

Electricity and Magnetism Electric forces hold atoms and molecules together Electricity controls our thinking, feeling, muscles and metabolIc processes. Electricity and magnetism underpin much of our current technology(e.g. computers). Electricity and magnetism are linked on a fundamental level

Electricity and Magnetism ➢ Electric forces hold atoms and molecules together. ➢ Electricity controls our thinking, feeling, muscles and metabolic processes. ➢ Electricity and magnetism underpin much of our current technology (e.g. computers). ➢ Electricity and magnetism are linked on a fundamental level

Key terms electric dipole closed surface electric flux electric charge surface integral electrostatics Gauss's law electron Gaussian surface proton Faraday' s icepail neutron experiment nucleus electric potential energy positive ion electric potential negative ion voltage ionization electron volt conductor equi potential surface insulator gradient point charge cathode-ray tube

electric charge electrostatics electron proton neutron nucleus positive ion negative ion ionization conductor insulator point charge Key terms: electric dipole closed surface electric flux surface integral Gauss’s Law Gaussian surface Faraday’s icepail experiment electric potential energy electric potential voltage electron volt equipotential surface gradient cathode-ray tube

§1 charges and coulomb’slaw 1.1 charges 1)Negative and positive 2) quantified(millikan) ne e=16×10C Fraction charge±e±=e 3 3 3)conservation(Franklin) 4)Invariance of charges

§1 charges and couloumb’s law 1. 1 charges 1) Negative and positive 2) quantified (millikan) e 1.6 10 C −19 Q = ne =  Fraction charge e 3 1  e 3 2  3) conservation (Franklin) 4) Invariance of charges

1.2 Couloumb's law 1)Model: point charge 2) Couloumb's law F=k21O2F-102-To ro-4兀Eor COULOMB kc=9×10Nm2/c2, En=885×1012c2/Nm2 F 21

1.2 Couloumb’s law 1) Model:point charge 2) Couloumb’s law q1 2 q r 21 r  F21  2 0 1 2 0 2 0 1 2 4 1 r r Q Q r r Q Q F k     = = k=9×109Nm2 /c2 ， 0=8.85×10-12c 2 /Nm2

Caution 1)valid for point charge in air 2)obey newton's law 3)in general Fe> F8 Henry Cavendish Experiment Gleichgewicht Torsionsfaden Gleichgewichts position 需( Position 2

3) in general Fe  Fg Caution: 1)valid for point charge in air 2) obey newton’s law Henry Cavendish Experiment

Quiz 1. Even though electric forces are very much stronger than gravitational forces, gravitational forces determine the motions in the solar system. Why? 2. When we approach another person, we are not aware of the gravitational and electric forces between us. What are the reason in each case?

1. Even though electric forces are very much stronger than gravitational forces, gravitational forces determine the motions in the solar system. Why? 2. When we approach another person, we are not aware of the gravitational and electric forces between us. What are the reason in each case? Quiz

s2 Electric field E 2.1 Electric field Electric source Electric field- Electric charge E、F Electric field for point charge F 1 goro 0 4丌六 qo4兀E0r Collection of point charge F E ∑Ek=∑ 4兀 r superposition of electric field

§2 Electric field E 2.1 Electric field Electric source Electric field Electric charge q0 F E   = Electric field for point charge 0 2 0 4 0 1 r r qq F    = 0 2 0 4 0 1 r r q q F E     = =     = = = k k k k k r r q E q F E 0 2 0 0 4 1 k k k      Collection of point charge superposition of electric field

Charge distribution dE 1 d e g-O 4丌Er ndl de dq da pdv de E g-O 4丌E Step to solve e. dE e=dE →dE→ → E= dE

Charge distribution 0 2 0 d 4 1 d r r q E    =   = 0 2 4 0 d r r q E    dq = dq r  E  d P dl dS dV Step to solve E: dq  dE   y x dE dE   Ex = dEx  Ey = dEy