Electrical Circuits

Formulae you need to know

Formula	Equation
Charge formula	$Q = I t$
Ohm's law	$V = I R$
Power formulae	$P = I V = I^{2} R = \frac{V^{2}}{R}$
Resistors in series	$R_{T} = R_{1} + R_{2} \dots$
Resistors in parallel	$\frac{1}{R_{T}} = \frac{1}{R_{1}} + \frac{1}{R_{2}}$
Potential divider 1	$V_{1} = (\frac{R_{1}}{R_{1} + R_{2}}) V_{S}$
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.