Electricity

Resistance

Any substance will conduct electricity if you put a big enough voltage across it: even air, which is normally an insulator, suddenly becomes a conductor when a powerful voltage builds up in the clouds—and that's what makes lightning.
When it comes to electricity, a binary label of conductor or insulator is useless, since anything with enough voltage will conduct electricity (even plastic). Instead, a better way to think about it is in terms of resistance level. Metal has low resistance, while plastic has high resistance.
- Resistors allow us to precicely control how much electrical current passes through it.
- an object with low resistance means that electrons are able to move more freely throughout it.
Ohm's Law - resistance is defined as the voltage required to make 1 amp flow through a circuit.
- Resistance can be determined by hooking up a multimeter to the circuit. The device feeds a known wattage current through the circuit and back into the device, and measures the volts that are received back into it.
level of resistance is measured in Ohms (Ω)

Falling between a conductor and insulator, a semiconductor has the quality that it decreases in resistance as its temperature rises (opposite of metals).

Incandescent lightbulbs (old-style)

these worked by having a filament with high resistance. The wire was so thin that the electricity has to fight to get through it, resulting in a lot of heat being given off, hence the name
This is similar to how toasters and kettles work. The idea is the same: shoot lots of electricity through an object with high resistance, causing it to heat up.

Analog Volume Knob (ex. radio)

The volume knob is actually part of an electronic component called a variable resistor. When you turn the volume down, you're actually turning up the resistance in the circuit that drives the radio's loadspeaker. With less current, there is less energy to power the loudspeaker.