# Electrical Circuits

Formulae you need to know

Formula Equation
Charge formula $Q=It$
Ohm's law $V=IR$
Power formulae $P=IV={I}^{2}R=\frac{{V}^{2}}{R}$
Resistors in series
Resistors in parallel $\frac{1}{{R}_{T}}=\frac{1}{{R}_{1}}+\frac{1}{{R}_{2}}$
Potential divider 1 ${V}_{1}=\left(\frac{{R}_{1}}{{R}_{1}+{R}_{2}}\right){V}_{S}$
Potential divider 2 $\frac{{V}_{1}}{{V}_{2}}=\frac{{R}_{1}}{{R}_{2}}$

### Potential Divider

A potential divider is a simple circuit with multiple resistors in series, where the voltage across the resistors is split proportional to the resistance.

### Nested Circuits

A circuit with nested series or parallel parts to it can be simplified "from inside out", much like evaluating brackets in a mathematical expression.

### Open Circuit

An open circuit is a circuit with an infinite resistance load connected to the power supply - which, in practice, means that the terminals of the power supply are not connnected.

### Short Circuit

A short circuit is the opposite of an open circuit - it's where there the terminals of the power supply are connected with no resistance. In practice, this usually means the terminals are connected by a wire or other conductive material with negligible resistance.