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where resistance in ohms and capacitance in farads yields the time constant in seconds or the cutoff frequency in hertz (Hz). The cutoff frequency when expressed as an angular frequency ( ω c = 2 π f c ) {\displaystyle (\omega _{c}{=}2\pi f_{c})} is simply the reciprocal of the time constant.
The equation is a good approximation if d is small compared to the other dimensions of the plates so that the electric field in the capacitor area is uniform, and the so-called fringing field around the periphery provides only a small contribution to the capacitance. Combining the equation for capacitance with the above equation for the energy ...
This results in the linear differential equation + =, where C is the capacitance of the capacitor. Solving this equation for V yields the formula for exponential decay: =, where V 0 is the capacitor voltage at time t = 0.
As a result, device admittance is frequency-dependent, and the simple electrostatic formula for capacitance, = , is not applicable. A more general definition of capacitance, encompassing electrostatic formula, is: [6]
For example, in charging such a capacitor the differential increase in voltage with charge is governed by: = where the voltage dependence of capacitance, C(V), suggests that the capacitance is a function of the electric field strength, which in a large area parallel plate device is given by ε = V/d.
The parasitic capacitance between the turns of an inductor (e.g. Figure 1) or other wound component is often described as self-capacitance. However, in electromagnetics, the term self-capacitance more correctly refers to a different phenomenon: the capacitance of a conductive object without reference to another object.
This circuit does not have a resistor like the above, but all tuned circuits have some resistance, causing them to function as an RLC circuit. An RLC circuit is an electrical circuit consisting of a resistor (R), an inductor (L), and a capacitor (C), connected in series or in parallel. The name of the circuit is derived from the letters that ...
where L, R and C represent inductance, resistance, and capacitance respectively and s is the complex frequency operator = +. This is the conventional way of representing a general impedance but for the purposes of this article it is mathematically more convenient to deal with elastance , D , the inverse of capacitance, C .