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Unformatted text preview: C APACITANCE A LI A LZAHRANI Capacitors are electric devices used for saving electric charge (energy) and enable us to use later. Any capacitor consists of two plates with equal and opposite charges on each one. The magnitude of charge kept in a capacitor is proportional to the voltage applied across the capacitor. That is ? = 𝐶? where 𝐶 is the capacitance . The SI unit of capacitance is Farad (F) which is (from the above equation) is Coulomb/Volt (C/V). Its symbol is C APACITANCE C APACITORS A parallelplate capacitor: two parallel plates having equal and opposite charges with plate are 𝐴 and separation by a distance ? . Its capacitance is 𝐶 = 𝐴𝜀 ? A cylindrical capacitor: two long coaxial cylinders of length 𝐿 and inner radius ¡ and outer radius ? . Its capacitance is 𝐶 = 2𝜋𝜀 𝐿 ln ? ¡ T YPES OF C APACITORS A spherical capacitor: two concentric spheres inner radius ? and outer radius ? . Its capacitance is 𝐶 = 4𝜋𝜀 ?? ? − ? An isolated spherical capacitor: for the previous capacitor, if ? → ∞ and ? = 𝑅 , we get an isolated spherical capacitor with capacitance 𝐶 = 4𝜋𝜀 𝑅 T YPES OF C APACITORS If capacitors be connected in parallel, the voltage across each capacitor is the same as the total voltage, but the charge on each is different. The equivalent capacitance of a group of capacitors connected in parallel is 𝐶 𝑒? = 𝐶 𝑖 𝑛 𝑖¡1 If capacitors be connected in series, the charge on each capacitor is the same as the total charge, but the voltage across each is different. The equivalent capacitance of a group of capacitors connected in series is ¢ 𝐶 𝑒?...
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 Spring '12
 1
 Physics, Capacitance, Charge, Energy, Electric charge, Electric Devices, ALI ALZAHRANI

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