Why is electrical resistance important?
Answer:
Electrical resistance impedes the flow of electrical current. There are a couple of reasons it is important to take into consideration.
First, in wires that carry current, the resistance causes some power loss - that power is lost as heat. If the resistance is too high for the current that is traveling on the wire, the wire can overheat, melting the insulation from insulated wires, or even causing heated wires to set fire to adjacent materials. So, if you are using wires to supply power to a device, you must size the wires properly to prevent this overheating. (This effect is actually used to make a toaster - the wires are sized to get hot enough to toast your bread, but not melt themselves.)
Secondly, resistance can be used to perform a useful function. The volume control on a radio (or iPod) is a resistor. The signal is placed across this resistor and a moving "tap" picks the signal off from some part. Move the tap closer to one end, and the volume goes up - move it closer to the other end and the volume goes down. In this example, the resistor "portions out" the signal to allow you to control the volume level.
To limit the current in the branch.
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