There is always some resistance in every circuit.
• A circuit is always made up of some wire, so there will be some resistance there.
• Even the battery has parts that offer resistance to the flow of
electrons.
• The only circuits that come near to zero resistance are
superconductors.
• This resistance that is from the parts of the circuit itself (especially
the battery) is called internal resistance.
• This internal resistance is usually drawn into a circuit
diagram (schematic) as shown in Figure 1.
• Notice the squiggly line just before the positive terminal of
the battery? That’s to show the internal resistance of the
circuit.
• That symbol, drawn any other place in the circuit, represents an actual resistor placed in the
circuit.
• A resistor is a device found in circuits that has a certain amount of resistance.
Why would you ever want to add resistance to a circuit by using a resistor?
• The most common reason is that we need to be able to adjust the current flowing through a
particular part of the circuit.
• If voltage is constant, then we can change the resistor to change the current.
I=V
R If “V” is constant and we change “R”, “I” will be different.
