What would be the percentage change in the energy stored in a capacitor, if the separation between the plates were to be decreased by 10 %, when voltage is constant?
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Answer:
Capacitance formed by two parallel plates decreases proportionally with the distance between the plates. The formula for capacitance is C = Permitivity-Between-Plates * Plate-Area / Plate-Distance. Therefore, multiplying the distance by 1.1 renders a new capacitance of only 90.9% when the plate separation is increased by 10%. Since the capacitor is charged and its energy is given by the squared potential energy formed by the involved charges is given by 1/2 * C * V squared, some of the charge in the capacitor will flow back to the voltage source since the capacitor’s voltage would have to increase in order to make 1/2 * Cprevious * Vprevious squared = 1/2 * Cdecreased *Vgreater squared. Alas, but would’nt that violate the Voltage source? Yes, it is referred to as a degenerate circuit condition. Fortunately, ideal voltage sources do not really exist. Instead, they always include a source resistance. Therefore, yes the capacitor voltage will slightly increase to discharge itself to its new lower level of energy storing capacity. As you can see, even simple questions about electrical issues very quickly become complex. For this reason, I strongly recommend that you get professional advice or enroll in an Electrical Engineering program..
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