What is Resistance? Resistance Explained
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Resistance is a measure of how hard it is for electrons to move through a part of the circuit.
The higher the resistance the more energy it takes to move the electrons through that area. Similar to running up a steeper and steeper hill.
As resistance increases and voltage is held steady the current in a circuit drops. By selecting the proper resistance we can control how much current flows in a circuit.
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Resistance is measured in a unit called Ohms whose symbol is the capital greek Omega and looks like this: Ω. One ohm is related to volts and amps by the equation \(\Omega = \frac{V}{A}\) which reads "One ohm is equal to one volt per amp." More on this in the next section.
Resistance is created in a circuit by using components called "resistors".
The resistance of a resistor is not written in numbers but coded onto coloured bands on the resistor's body. You will need to be able to read these codes but you will not need to memorise the rules, you will (probably) always have a chart nearby you can check.
Resistors can be found in (basically) any value however your common resistors will range from 100Ω to 1 million Ω.
As you'll learn in more detail later you don't need to buy the exact resistor you need, you can combine several resistors together in various ways to create a new resistor with a different resistance. You can get a new resistance which is an increase, decrease, or something in between depending on how you connect your resistors together.
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Wires have resistance however in a circuit diagram the wires we draw are assumed to have absolutely no resistance. If the wires' resistance needs to be taken into account a resistor is drawn on the wire to represent its resistance.
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Your resistor will have either four or five bands. The following graphic will show you how to calculate its resistance:
To determine which side to read from on a resistor check the spacing between the last and second to last bands, this will always be the largest gap. It's sometimes hard to tell with a real resistor but practice and it'll become second nature.
practice problems