同济大学：《大学物理》课程教学资源（电子教案，英文版）第十二章 电场与电势（下）

Electric potential 100004DECIMILA 281 CAMP AA000000A BANCA DITAUA AA000000A

Electric potential

Agenda today electric potential equipotentials relationship between electric potential and field strength electric potential and electric field around conductor

Agenda today electric potential equipotentials relationship between electric potential and field strength electric potential and electric field around conductor

Work done by electric force: dA=q,E·dl=q,Ecos0dl E= 4πe,r2 a dA= 9o9 cos0 dl= 99 _dr 4π6，r1 4π6.1

Work done by electric force: q b a r  r   dr  dE   dA q E dl q E dl  o   o cos   2 4 r q E   o  dr r q q dl r q q dA o o o o 2 2 4 cos 4       

The work done by electric force is independent of the path taken by the charge,thus static electric force is conservative force. A=fq.E.dT=0

            o a b o r r o o a b r r q q dr r q q A b a 1 1 4 4 2     The work done by electric force is independent of the path taken by the charge, thus static electric force is conservative force.    0 l o A q E dl     0 l E dl  

Electric potential Electric potential energy Point charge q moves in static electric field with no other force exerted on the charge except the static electric force from a to b: △9==qE

Electric potential Electric potential energy Point charge q moves in static electric field with no other force exerted on the charge except the static electric force from a to b:

Electric potential difference: - If point a is chosen as the reference point: U-NEalEa Thus,electric potential difference can expressed as Uba=Up-Ua In most cases,U is set as zero,when r approaches infinite

Electric potential difference: If point a is chosen as the reference point: Thus, electric potential difference can expressed as Uba=Ub -Ua In most cases, U is set as zero , when r approaches infinite

The unit of electric potential Volt(V) 1V=1J/C 1V/M=1N/C

The unit of electric potential Volt(V) 1V=1J/C 1V/M=1N/C

Electric potential distribution for field of one single charge U.-d-北 4πe,'a An8oYa

Electric potential distribution for field of one single charge o a a r q U 4  

Potential in a system of charges 1 If the electric field is known,the definition equation should be used 2 If the electric field is unknown,then use the superposition principle U=-

Potential in a system of charges 1 If the electric field is known, the definition equation should be used 2 If the electric field is unknown, then use the superposition principle

ll FIGURE P29.71 shows a thin rod with charge O that has been bent into a semi- circle of radius R.Find an expression -Center for the electric potential at the center. Charge Q