81-演示文稿-电场能量（双语）.pptxVIP

9. Energy in Electrostatic Field Under the influence of electrostatic fields, a positively charged body will be moved along the direction of the electric field. In this case, work is being done by the field. In order to do this work the electrostatic field must lose energy, implying that the electrostatic field has stored energy. If the charged body is moved into the electrostatic field from infinity by an applied force, work is being done against the electric force. This work will be become part of the energy stored in the field, and the total energy of the electrostatic field will be increased. The total energy stored in an electrostatic field can be determined from the work done to assemble the charges giving rise to the field. First, we calculate the energy of an isolated body with charge Q.;Q;The electric potential ? of an isolated conductor is equal to the ratio of the charge q to the capacitance C, i.e.;Q1 , Q2 ,?, Qn;If the charge is distributed in a volume, on a surface, or at a line, considering dq ? ? dV ? ?S dS ? ?l dl , then the total energy of the body with the distributed charge can be written accordingly as;;The above equation for the stored energy can be written as;;Example. Find the energy of a conducting sphere with radius a and charge Q. The permittivity of the dielectric around the conductor is ? . Solution: Three methods can be used. (1) The electric potential of a conducting sphere with radius a and;(3) The electric field intensity caused by a conducting sphere with