Electricity passes through electric conductors and is hindered by electric insulators.

Current is the flow of free electrons moving between atoms in electrically conductive materials. Static electricity occurs when objects are electrically charged. An atom's total charge is dependant on its relative charges (positive nucleus vs. negative electrons).

Materials obtain charge by acquiring atoms from other materials.

## Current

The flow of charge in a material that allows electrons to move freely. Measured in amperes.

### Unit Current

$ampere = (\approx 6.25) \times 10^{18}$

## Coulomb

Unit of charge over a time of $n$ seconds.

$C = As$

(A current of $1A$ passing in $1s$ equals $1C$)

## Batteries and Cells

Electrons in any circuit transfer energy from the energy source (battery) to the components on the circuit. A chemical process inside of a battery's cells, involving electrodes and electrolytes, is responsible for keeping the current alive.

## Voltage

The power in watts that a cell can supply to its circuit. e.g. a 12 volt source delivers 12 watts of power for every ampere of current passing through it. Also called potential difference.

$V = \frac W A$

The voltage delivered by the battery is equal to the sum of voltages around the circuit.

## Electric Circuits

### Components in series

The same current passes through all components

### Components in parallel

The current shared by all components in parallel. However their voltage remains the same.

### Resistance and Resistors

Components that transform kinetic energy of electrons to waste heat by slowing them down. The power source acts as resistor because without one current can not flow (lack of potential difference (voltage)).

$\Omega = \frac V A$

### Variable Resistors

Components that change the current withou changing the voltage. Usually a coiled wired with a moving output that may touch the wire at any point.

### Diode

A component that restricts the flow of current in one direction.

## Electrical Power

Since $voltage = \frac {power}{current}$ it follows that

$power = voltage \times current$

## Frequency

How often a current reverses in an alternate current circuit per second.

### Unit Frequency

Hertz

$Hz = cycle/s$