Chapter 22 Capacitance, Dielectrics, Electric Energy Storage 22-2 Capacitance P526-529 1. Definition of capacitance of isolated conductors 电荷q2q3q4q ng ++ 电势v2v3v4v….ny O/V=const q C
Chapter 22 Capacitance, Dielectrics, Electric Energy Storage 22-2. Capacitance P526-529 1. Definition of capacitance of isolated conductors + + + + + + + + +Q V 电荷 电势 q V 3q 3v 2q 2v 4q 4v nq nv …. …. v q Q /V = const V Q C =
Chapter 22 Capacitance, Dielectrics, Electric Energy Storage The capacitance is a measure of how much charge must be put on the plates to produce a certain v between them: The greater the capacitance, the more charge is required. Its value(固有容电本领) depends only on the geometry(几何因素) of plates, dielectric propert!y and not on their e or v. The value of capacitance depends only on the size, shape and relative position of the two conductors, also on the material that separates them
Chapter 22 Capacitance, Dielectrics, Electric Energy Storage The value of capacitance depends only on the size, shape and relative position of the two conductors, also on the material that separates them. The capacitance is a measure of how much charge must be put on the plates to produce a certain V between them: The greater the capacitance, the more charge is required. Its value (固有容电本领) depends only on the geometry (几何因素) of plates, dielectric property and not on their Q or V
Chapter 22 Capacitance, Dielectrics, Electric Energy Storage 2. Unit of capacitance SUnit: coulomb per volt farad(F)(法拉) 1微法(μF)=106F 1皮法(pF)=106μF=1012F 3. The capacitance of an isolated conducting sphere FOR 41E。R R
Chapter 22 Capacitance, Dielectrics, Electric Energy Storage 2. Unit of capacitance R R Q Q V Q C 0 0 4π 4π = = = R Q 3. The capacitance of an isolated conducting sphere 1微法（F）=10-6F 1皮法（pF）= 10-6 F = 10-12 F SI unit: coulomb per volt farad (F) (法拉)
Chapter 22 Capacitance, Dielectrics, Electric Energy Storage 4. The capacitance of capacitors(电容器的电容量) 孤立导体的电容很小,用它作电容器不适合。用 两个导体组成的电容器可实现较大的电容。 电容器电容 g oc AB g=cU AB Q C B AB B
Chapter 22 Capacitance, Dielectrics, Electric Energy Storage 4. The capacitance of capacitors (电容器的电容量） 孤立导体的电容很小，用它作电容器不适合。用 两个导体组成的电容器可实现较大的电容。 电容器电容 A B U AB Q U U Q C = - = VB VA -Q + Q q UAB q = CUAB
Chapter 22 Capacitance, Dielectrics, Electric Energy Storage 实际中屏蔽不一定要求很高故在工艺上用两无限大 平板代替AB导体。 绝缘纸 C 金色铂 Insulator Two plates are rolled into the form of a cylinder with paper or other insulator separating the plates
Chapter 22 Capacitance, Dielectrics, Electric Energy Storage 实际中屏蔽不一定要求很高故在工艺上用两无限大 平板代替AB导体。 绝缘纸 金色铂 C Two plates are rolled into the form of a cylinder with paper or other insulator separating the plates