![]() ( e x is e to the x power, where e =2.718, the base of the natural logarithm) The product RC is called the time constant (whose units are seconds) and is usually represented by the Greek letter τ. V (t ) = A + Be RC where constant A is the final voltage and constant B is the difference between the initial and the final voltages. RC Circuits An RC (resistor + capacitor) circuit will have an exponential voltage response of the form !t Q = CV Since Q is the integration of current over time, we can write: v (t ) =ĭifferentiating this equation, we obtain the I-V characteristic equation for a capacitor:Ģ. The voltage V across the capacitor (capacitance C) is directly proportional to the charge Q stored on the plates: When current flows into one plate of a capacitor, the charges don't pass through (although to maintain local charge balance, an equal number of the same polarity charges leave the other plate of the device) but instead accumulate on that plate, increasing the voltage across the capacitor. Recall that a current is a flow of charges. Practical capacitor values usually lie in the picofarad (1 pF = 10-12 F) to microfarad (1 ♟ = 10-6 F) range. The unit of capacitance is the farad (coulomb/volt). ![]() ![]() Capacitors A capacitor is a passive electronic component that stores energy in the form of an electrostatic field.
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