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PH 112 Capacitance January 27, 2005 MJM Name _____________________ Box _______ Capacitance is defined as C = q/V. A capacitor can be any two conductors where we may have equal and opposite charges q, and a potential difference V between the conductors. When two capacitors C1 and C2 are attached in series, the equivalent capacitance C is given by 1/C = 1/C1 + 1/C2. +q C1 V1 +q C The sketch at the right shows two capacitors in series and their equivalent capacitance C. Two features are very important 1) each capacitor has the same charge q 2) the potential difference V =V1 + V2 V +q C2 V2 Use the relations V = V1 + V2 and q/V1 = C1, etc. to show that 1/C = 1/C1 + 1/C2. For capacitors in parallel, V1 = V2 = V and q = q1 + q2. Use these relations to show C = C1 + C2. +q1 C1 V1 Find the equivalent capacitance in F of the three capacitors shown in the sketch. +q2 C2 +q C V2 V a 3 F 6 F Cab = b 5 F