3.2 Resistors

This is the second week of Module 3 of the Navy Basic Electricity and Electronics series. Last week was:

• 3.1 What is resistance?

This week is on resistors. I chuckled because so much is now done on integrated circuits that have billions of items on a small chip. I probably haven't seen a resistor in decades. But poking around I see that visible resistors still find their way onto circuit boards.

• Basically, a resistor is a circuit component that limits or controls the amount of current flow. Otherwise, other components might be damaged or might not function optimally. Think of slowing down the flow of a raging river, except the river is electrical current.  
• Resistors are rated in ohms (see the previous post). They are also rated in watts, which tells you how much power they can take without getting damaged.
• One type used to be made out of a mixture of carbon and clay (composition resistor). These could change in value with age and were not good for carrying large currents.
• Another type were e-wound resistors, with varying length of wire wrapped around a ceramic tube and painted with an insulating glaze. They could carry more current and could be more accurate. But they also used to be more expensive.



Taken from Wikipedia

• The symbol for a resistor with a fixed value is in the diagram to the right.
• "Tapped" resistors and sliding-contact resistors provide the possibility of varying the amount of resistance as desired. Tapped resistors have multiple connections available. The amount of resistance depends on which "tap" you are connected to.
• The sliding contact resistor can be slid to change the resistance (so it's a "variable" resistor). Once set, however, it usually isn't changed.
• There are also other kinds of variable resistors. The one is the potentiometer, which has three connections with three different resistance options (see picture below).
• The other is the rheostat, which used to have a movable contact in between two connections.

From Wikipedia