【双语物理】静电场_3_capacitance_dielectrics.docxVIP

A capacitor is a device which stores electric charge.-Examples include storing electric potential energy, delaying voltage changes when coupled with resistors, filtering out unwanted frequency signals, forming resonant circuits and making frequency-dependent and independent voltage dividers when combined with resistors. -During the charging process, a charge Q is moved from one conductor to the other one, giving one conductor a charge +Q, and the other one a charge -Q. A potential difference ?V is created, with the positively charged conductor at a higher potential than the negatively charged conductor is. Note that whether charged or uncharged, the net charge on the capacitor as a whole is zero. Q=C|?V|, where C is a positive proportionality constant called capacitance. *Physically, capacitance is a measure of the capacity of storing electric charge for a given potential difference ?V. It depends only on geometric/physical factors. The SI unit of capacitance is the farad (F): 1 F = 1 C/V A typical capacitance is in the picofarad (1pF=10-12F) to millifarad range (1mf=103μF=10-3F).Calculation: Capacitance*Problem-Solving Strategy:Identify the direction of the electric field using symmetry;Calculate the electric field everywhere;Compute the electric potential difference ?V;Calculate the capacitance C using C=Q/|?V|.1* Parallel-Plate Capacitor 2* Cylindrical Capacitor 3* Spherical Capacitor 4* Single “isolated” charged spherical conductorCapacitors in Electric Circuits*Parallel *Series Storing Energy in a CapacitorDuring the charging process, the battery does work to remove charges from one plate and deposit them onto the other. Suppose the amount of charge on the top plate at some instant is +q, and the potential difference between the two plates is |?V|= q/C. To dump another bucket of charge +dq on the top plate, the amount of work done to overcome electrical repulsion is dW=|?V|dq. If at the end of the charging process, the charge on the top plate is