## Important Concepts

We’re going to dive deeper into resistors and resistor networks later, but:

• Resistors are electronic components made of materials that restrict the flow of electricity.
• Resistance is measured in ohms, often denoted as `Ω`.
• Ohm’s law states that the resistance provides a proportional reduction of current flow and is codified as:
• `Voltage = Amperage * Resistance` or `V = I*R`
• `Amperage = Voltage / Resistance` or `I = V/R`
• `Resistance = Voltage / Amperage` or `R = V/I`
• Where `I` is amps, `R` is ohms, and `V` is voltage.
• Resistors have a power rating which specifies the amount of power (wattage) they can safely handle.
• In addition to the standard definition of a watt (`volts * amps`), power can be calculated when only volts or amps and resistance is known:
• When amperage (current) and resistance is known: `P = I^2 * R`
• When voltage (force) and resistance is known: `P = V^2 / R`
• Resistors wired in series (end-to-end) have a total resistance which is the sum of the resistance of each resistor.
• Conductance is the reciprocal of resistance, `(1/R)`, and is measured in siemens (S), but most often abbreviated as `G`.
• Resistors wired in parallel have a total resistance which is the sum of the conductance (in siemens) of each resistor, and then converted back to resistance.
• Axial resistors are color coded to aid in identifying them. See this chart for reference.
• Resistors have a tolerance which specifies a range that their actual resistance falls into.
• Resistors come in a set of values that covers the range of possible values, adjusted for tolerance, with only small overlap.
• Breadboards reduce prototyping complexity by allowing you to create circuits without soldering.
• A pull-up resistor provides a default `HIGH` value at an input in a circuit by connecting the input to a voltage source and allowing a small amount of current to flow.
• A pull-down resistor is the opposite of a pull-up, and provides a default value of `LOW` at an input in a circuit.
• Pull-up and pull-down resistors are one of the most common tools in circuit design.
• Pull-ups and pull-downs with smaller resistance values are known as strong pull-ups and pull-downs, and act quicker than weak pull-ups and pull-downs, which have a larger resistance value.

## Part 5 - DC Circuit Analysis

These docs are open source. If you find an issue, please file a bug, or send us a pull request. And if you want to contribute, we'd love that too!