# Ohm's Law

### Reference Material

• Horowitz & Hill, The Art of Electronics, 2nd Ed., Ch. 1

## Ohm’s Law

${\displaystyle V=IR,\,\!}$

where ${\displaystyle V}$ is voltage, measured in Volts (${\displaystyle V}$), with typical values ranging from ${\displaystyle mV}$ (into an oscilloscope) to ${\displaystyle kV}$ (power lines, severe arcing danger); ${\displaystyle I}$ is current, measured in Amperes (${\displaystyle A}$), typical values ranging from ${\displaystyle mA}$ (relatively safe for bench-top work) to ${\displaystyle A}$ (very dangerous); ${\displaystyle R}$ is resistance, measured in Ohms (${\displaystyle \Omega }$), typical values ranging from ${\displaystyle \Omega }$ (power resistors dissipating a lot of power) to ${\displaystyle M\Omega }$ (almost a no-connect).

## Resistor

Symbol for a resistor in schematics

### Resistors in Series

Resistors in series add:

Resistors in series

${\displaystyle R=R_{1}+R_{2}+\dots \,\!}$

### Resistors in Parallel

Resistors in parallel add reciprocally:

Resistors in parallel

${\displaystyle R={\frac {1}{{\frac {1}{R_{1}}}+{\frac {1}{R_{2}}}+\dots }}\,\!}$