Obtain an expression for equivalent capacitance when three capacitors C1,C2 and C3 are connected in series.
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Solution
Consider that three capacitors having capacitance C1,C2 and C3 are connected in series to each other shown in the figure above, Consider that +q charge is given to first plat of first capacitor. By induction a charge (−q) will produce at internal surface of second plate of this capacitor and so on. Consider that potential between the plates of capacitor are C1,C2 and C3 respectively so, V1=qC1,V2=qC2 and V3=qC3 Now V=V1+V2+V3 ∴V=qC1+qC2+qC3 ...(i) If equivalent capacitance of combination of capacitors is C then V=qC ...(ii) By equations (i) and (ii), we get qC=qC1+qC2+qC3 ⟹1C=1C1+1C2+1C3