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The cutoff frequency when expressed as an angular frequency (=) is simply the reciprocal of the time constant. Short conditional equations using the value for / (): f c in Hz = 159155 / τ in μs τ in μs = 159155 / f c in Hz. Other useful equations are:
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 ...
The natural frequency (that is, the frequency at which it will oscillate when isolated from any other system, as described above) is determined by the capacitance and inductance values. In most applications the tuned circuit is part of a larger circuit which applies alternating current to it, driving continuous oscillations.
Like the one-dimensional harmonic oscillator problem, an LC circuit can be quantized by either solving the Schrödinger equation or using creation and annihilation operators. The energy stored in the inductor can be looked at as a "kinetic energy term" and the energy stored in the capacitor can be looked at as a "potential energy term".
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.
The formula for capacitance in a parallel plate capacitor is written as C = ε A d {\displaystyle C=\varepsilon \ {\frac {A}{d}}} where A {\displaystyle A} is the area of one plate, d {\displaystyle d} is the distance between the plates, and ε {\displaystyle \varepsilon } is the permittivity of the medium between the two plates.
Switched-capacitor circuits are analysed by writing down charge conservation equations, as in this article, and solving them with a computer algebra tool. For hand analysis and for getting more insight into the circuits, it is also possible to do a Signal-flow graph analysis, with a method that is very similar for switched-capacitor and ...
Wien's bridge is used for precision measurement of capacitance in terms of resistance and frequency. [3] It was also used to measure audio frequencies. The Wien bridge does not require equal values of R or C. At some frequency, the reactance of the series R 2 –C 2 arm will be an exact multiple of the shunt R x –C x arm.