tailieunhanh - PHYSICS 3 (ELECTRICITY AND MAGNETISM) - CHAPTER 2

ELECTRIC ENERGY AND CAPACITANCE Tiềm năng khác biệt và điện tiềm năng 1) năng lượng tiềm năng điện, điện thế khác nhau và tiềm năng điện Hãy xem xét các hệ thống được thành lập bởi các Q phí và q trong hình. . E điện trường do Q phí E = Q 4πε o r 2 [Vm-1], [NC-1] () F lực tĩnh điện về tội q F = QE = QQ 4πε hoặc 2 [N] () Khi phí q được phát hành từ điểm A, nó di chuyển từ Q, dọc theo dòng điện trường. Sự mất mát năng lượng tiềm. | Electricity and Magnetism 18 Chapter 2 ELECTRIC ENERGY AND CAPACITANCE Potential Difference and Electric Potential 1 Electric potential energy electric potential difference and electric potential Consider the system constituted by the charges Q and q in Fig. . The electric field E due to the charge Q E J Vm-1 NC I 4nSor The electrostatic force F on the charge q F qE q j N 4neor When the charge q is released from point A it moves away from Q along the electric field line. The loss in potential energy of the system as the charge q moves from A to B is the work done by the electric force dW F .dĩ Fdr -qQd2 4n8or W ri-qQdrr --1 Ì J r 4neor 4n8o I rA rB The work done by the electrostatic force is path independent. It depends only on the initial point A and the final point B and is the same for all paths between A and B. Fig. The change in the potential energy of the system AU Ub - Ua -W where UA and UB are the potential energy of the system when the charge q is at A and B respectively. When q moves from A to B AU 0 the electric force F does work W 0 and the system loses energy. If we set the potential energy of the system UB 0 at infinity . rB x the reference point of zero potential at infinity then it follows from and that Electricity and Magnetism 19 Ua q J 4nSorA The electric potential the potential energy per unit charge at point A is defined as Va Ua J C V q 4n80rA The electric potential difference between A and B is the difference in potential energy per unit charge AV AU -W -Q- T Ì Vb - Va J C V q q 4nSo I rA rB 2 Equipotential surfaces The points on an equipotential line all have the same electric potential. Equipotential lines are always perpendicular to the electric field. In three dimensions the lines form equipotential surfaces. Movement along an equipotential line or an equipotential surface requires no work because such movement is always perpendicular to the electric field. For a point charge the .