in πŸ““ Notes

Physics

Voltage

The voltage is the difference in electrical potential between two points. It’s measured in Volts, $V$.

Capacitor

  • A capacitor can store electrical charge.
  • Buffers voltage changes.
  • Builds up charge on the two sides of an insulator.

Capacitance

Capacitance refers to the ability of a capacitor to store charge. Represented in Farads, $F = A^2 s^4 kg^{βˆ’1} m^{βˆ’2}$.

  • ⬆ area –> ⬆ capacitance

Parallel Plate Capacitor

The formula for the capacitance of a parallel plate capacitor is as follows:

$$C=\epsilon\frac{A}{d}$$

Where:

  • $A$ is the area of overlap of the two plates in $m^2$.
  • $d$ is the separation between the plates in $m$.
  • $\epsilon$ is the permittivity.

Resistance

Resistance is how much a conductor opposes the [current][#current]. The unit is Ohm, $\Omega$.

Conductance

Conductance is the inverse of resistance, representing the ease with which an electric current passes. The unit is Siemens, $S = \Omega^{-1}$.

$C = \frac{1}{R}$

Current

Current is the flow of charge. Usually represented by $I$. Measured in Amperes.

Ohm’s Law

$$I = \frac{V}{R}$$

Where:

Time Constant

  • How much time it takes to charge 63%

$$\tau=RC$$

  • $R$ in Ξ© cm
  • $C$ in F

Length Constant

  • Distance it takes for a potential change to fall off ~37%.

$$\lambda=\sqrt{\frac{R_{membrane}}{R_{axial}}}$$

  • $R_{membrane}$ in Ξ© cm
  • $R_{axial}$ in Ξ© / cm

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