Resistors> <#5625,5132><!Resistors> are like a bumpy dirt road. Cars can still travel it. But the bumps slow them down. The bumpier the road, the slower the driving. Resistors are devices used to slow down the electric <#5967,6><!current>. (Resist means to “fight against.”) They can slow the electric current just a little or a lot.
How much is a little resistance? How much is a lot? A tool called an <#5626,5135><!ohmmeter> measures the amount of resistance. The unit of measurement is called an <#5627,5142><!ohm>. A few ohms of resistance (slow-down of electricity) wouldn’t keep a bulb from lighting. But a few million ohms is a major slow-down. No bulb can light when the flow of electricity slows that much.
Insulators are the ultimate resistors. They slow the flow of current to a stand-still - zero current.
Variable resistors let you vary, or change, the amount of their resistance. A good “sound” use of variable resistors is volume control on a radio. At zero volume, a variable resistor allows no current to flow through (a LOT of resistance). So no sound comes out. Slowly move the volume dial to one, then two, then . . . ten! And as you turn the dial, the variable resistor allows more and more current to flow through (with less and less resistance). The sound gets louder, bit by bit.
Sometimes, scientists like to measure the opposite of resistance. “Conductance” measures how easily electric current will flow through a material. It’s the exact reverse of resistance, and the unit of measurement is called the <#5628,5143><!mho> (which is the exact reverse of ohm).
