82 Capacitance and DielectricsP26.10With θπ=, the plates are out of mesh and the overlap area is zero. Withθ=0 , the overlap area is that of a semi-circle, πR22. By proportion, theeffective area of a single sheet of charge is πθ−afR22When there are two plates in each comb, the number of adjoiningsheets of positive and negative charge is 3, as shown in the sketch. Whenthere are Nplates on each comb, the number of parallel capacitors is 21N−and the total capacitance isFIG. P26.10CNANRdd=−∈=−∈ −=2200202afafafafafeffectivedistance.P26.11(a)Ckeba==×=A250 02 8 99 102689727258ln..ln...chejnF(b)Method 1:∆Vkbae=FHGIKJ2λln×=××FHGIKJ=−−−qVA810 10162 102 8 99 101 62 103026797....ln...C50.0 mCmkV∆ejMethod 2:∆VQC××=−−268 1069... kVP26.12Let the radii be band awith ba=2 . Put charge Qon the inner conductor and –Qon the outer.Electric field exists only in the volume between them. The potential of the inner sphere is
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