Fundamental Electrical and Electronic Principles, Third Edition

96 Fundamental Electrical and Electronic PrinciplesC 1C 2C 3C 4Fig. 3.20so, the total for the complete arrangement C 1 4, but we canexpress 4 as (5 1) so the total capacitance isC1εεA51 o r ( )dfaradIn general therefore, if a capacitor has N plates, the capacitance isgiven by the expression:C1εεAN1 o r ( )dfarad(3.16)Since the above equation applies generally, then it must also apply tocapacitors having just one pair of plates as previously considered. Thisis correct, since if N 2 then ( N 1) 1, and the above equationbecomes identical to equation (3.12) previously used.Worked Example 3.13Q A capacitor is made from 20 interleaved plates each 80 mm by 80 mm separated by mica sheets1.5 mm thick. If the relative permittivity for mica is 6.4, calculate the capacitance.AN 20; A 80 80 10 6 m 2 ; d 1.5 10 3 m; ε r 6.4C1εε AN1 o r ( ) faradd8. 854 10126.4 6400106191.5103soC 46 . nF AnsWorked Example 3.14QA 300 pF capacitor has nine parallel plates, each 40 mm by 30 mm, separated by mica of relativepermittivity 5. Determine the thickness of the mica.