Nuts and Volts - June 2014

60 June 2014

with fewer electrons (hey, that’s what quantum physicists say if you read between the lines). Areas with more electrons are said to have a higher electric potential relative to areas with fewer electrons. Figure 1 shows this with holes at different depths along the side of a bucket. This potential difference (more electrons in one area and less in another) can be thought of as a force that pushes electrons from one place to another. Voltage is a measure of the electric potential difference between two areas that have different amounts of electrons. Water will run down hill if it can run down hill, and electrons will spread out from higher electron density regions to lower electron density regions if they can spread out.

Electric Current = Amps

We think of current as the amount of water moving past in a stream. The Gulf Stream, for example, has a lot more water moving along than what comes out of your bathroom faucet. A bolt of lightning has a lot more electrons moving past than the spark of static electricity your older brother applies to your ear after sliding his bunny slippers across the wool carpet in the hall on a dry day. The amount of electric current is referred to as amperes or amps. Figure 2 uses the water bucket metaphor with larger holes allowing greater current. Pressure is the same, but as the holes get bigger you get a greater current.

Electric Resistance = Ohm (Ω)

For the water analogy, we can think of resistance as being caused by the diameter of the hole. Note that in Figure 2 more current is due to different size holes — bigger hole, less resistance, more water.

For the resistors in the projects kit (available at the NV

Webstore), the higher the number, the more the resistance.

So, you can think about the 10K Ω resistors as having a smaller electric hole and thus passing less current than 1K Ω resistors which have a bigger hole and pass more current. Materials with low resistance are known as conductors, while materials with high resistance are known as insulators. Electrons move easily in some things such as copper wire (a good conductor), but are stopped cold by some things such as glass (a good insulator). Copper has very low resistance — jumper wires can have near zero ohms of resistance (about one ohm per 62 feet), while glass can have millions of ohms of resistance.

Ohm’s Law

Georg Simon Ohm wrote a rule to account for observations of voltage (volts), current (amps), and resistance (ohms). We typically see this rule as voltage is equal to current times resistance: Volts = Amps Ohms Voltage equals current times resistance.