Part 4 Review

Important Concepts

In this part we learned what resistance means, electrically. What a resistor is and how to use them.

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.