in π Notes

# Physics

Table of Contents

2 min read

## 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, $F = A^2 s^4 kg^{β1} m^{β2}$.

- β¬ area –> β¬ 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:

- $I$ is the Current
- $V$ is the Voltage
- $R$ is the Resistance

## 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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