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Wiring Fundamentals: Resistance

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00:00 - Resistance is a measure of how hard it is for the electrons to flow in response to an applied electrical pressure.
00:06 It can be thought of as a restriction the tap imposes on the flow of water when it's only partially open.
00:13 If we just barely crack the tap open and get a trickle of water coming out, this is a low flow rate as the tap is imposing a high resistance.
00:20 Alternatively if we open the tap fully, it will allow the maximum flow rate the main system can supply.
00:26 This is a high flow rate as the tap is now imposing a low resistance.
00:30 Back in the electrical world, the same concept applies.
00:33 We have discussed connecting one end of the wire to the positive terminal of a 12 volt battery and the other end to the negative terminal.
00:39 You should never actually do this however as the wire is like a pipe with the tap fully open.
00:45 It has a very low resistance to flow, so a very large and dangerous current will flow.
00:51 If we put something in the middle of the wire that the electrons find it harder to flow through, like a fuel injector for example, the resistance the fuel injector imposes, will decrease the current flow.
01:01 The key concept to grasp here is that different resistances cause different levels of current to flow in response to the same applied electrical pressure.
01:10 In our plumbing analogy, the mains pressure never varied from 60 psi but the flow of water varied in response to how far we opened the tap.
01:19 This is why most electrical devices in a vehicle have a pretty narrow range of voltages that they operate at.
01:24 They're designed with a specific resistance that allows the right amount of current to flow through the device for it to operate correctly.
01:30 This can only be done if the designer knows the narrow voltage range that the device will operate at.
01:36 Luckily for our industry we know this is typically between 11 and 14.2 volts.
01:42 If we apply a voltage that is either too low or too high, the wrong amount of current will flow and the device will either not work as expected or worse, be permanently damaged.
01:51 Another idea I'd like to touch upon when talking about resistance is the term load.
01:56 Electrical devices in the car are often referred to as placing a load on the electrical system.
02:01 This term describes how hard the electrical system has to work to supply the required current to the device.
02:07 As a device with a higher resistance will require only a small current, it's actually only placing a small load on the electrical system of the vehicle.
02:15 So load can be thought of as the opposite of resistance.
02:19 The lower the resistance, the more current flows, and the greater the load.
02:23 When you are reading or writing documentation, resistance has a unit of ohms, and a symbol of either a capital R, or a capital greek omega.

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