Terminology for today Edge effect energy density polarization dipole Displacement orientation onIc Bound bound charge free charge Volume density surface density electric displacement Linear isotropic permittivity susceptibility Continuity condition electrets anisotropy
Terminology for today Edge effect energy density polarization dipole Displacement orientation ionic Bound bound charge free charge Volume density surface density electric displacement Linear isotropic permittivity susceptibility Continuity condition electrets anisotropy
HH》 Calculation: 1) Gauss theorem gives e=o/8 2)The potential difference between two plates =E●d=ol/E 3 The total charge of the plate Q=0·A 4) Therefore, the capacitance is C=Q/V=80A/d
Calculation: 1) Gauss theorem gives : 0 E = / 2) The potential difference between two plates: V E d d o = • = / 3) The total charge of the plate Q = • A 4）Therefore , the capacitance is C = Q/V = 0 A/ d
2.2.5 Capacitors in parallel Because Q=g1+Q2+……+Qn=C+C2+…+Cn Therefore C=C1+C2+……+ 2.2.6 Capacitors in series Because V=Q/C1 V2=Q/C2 V=Q/C Therefore —+ 2
2.2.5 Capacitors in parallel Because Q = Q1 +Q2 +......+Qn = C1 V +C2 V +....+Cn V Therefore C = C +C + +Cn ....... 1 2 2.2.6 Capacitors in series Because 1 1 V = Q/C 2 2 V = Q/C V n Q Cn = / ………….. Therefore, C C C Cn 1 ........... 1 1 1 1 2 = + + +
2. 2. 7 Energy stored in a charged capacitor Since dw=vdq==dQ After the integral w=-Cv2 Problem Using above result to derive energy stored inside a parallel-plated capacity with parameters of A, d and E. You may Discuss the significance of so called energy densi ity within a capacity
2.2.7 Energy stored in a charged capacitor dQ C Q Since dw =Vdq = After the integral, 2 2 1 w = CV Problem Using above result to derive energy stored inside a parallel-plated capacity with parameters of A,d and E. You may Discuss the significance of so called energy density within a capacity
2.3 Insulator-dielectrics(Insulator )in Electrostatic Field 2.3. 1 The polarization Character of dielectrics The concept of bound charge, molecular dipole momentum . Displacement polarization . Orientation polarization clonic polarization 2.3.2 The density of bound charges of dielectrics volume density P=-VeP The proof: From the conservation of charges Discussion: for any Q+POds=0 linear dielectrics only surface density Surface density S exists. Why? =P·n The proof: From the definition, d=onds=Odl o ds
2.3 Insulator-dielectrics (Insulator) in Electrostatic Field 2.3.1 The polarization Character of dielectrics The concept of bound charge, molecular dipole momentum •Displacement polarization •Orientation polarization •Ionic polarization P=np 2.3.2 The density of bound charges of dielectrics • volume density b P = −• The proof: From the conservation of charges, + • = 0 s Q P ds •Surface density b P n = • The proof : From the definition, dQ ds Qdl ds b = = • Discussion: for any linear dielectrics, only surface density exists. Why?