There’s a very good reason why I am not a fully-qualified Electronics Engineer, pushing forward the frontier of knowledge about the next-generation semi-conductors, inventing the next Internet-ready household appliance, and being admired by all the women.<\/p>\n
The reason is that electricity doesn’t work.<\/p>\n
Well, what I really mean is, electricity doesn’t work they way they teach you it works when you are young.<\/p>\n
The rules they teach you are lies; the analogies they give you are confusing.<\/p>\n
Here’s how I remember it:<\/p>\n
Electricity Expert:<\/strong> Kirchoff’s Rules are the basis of electronics. For example, one of these rules says the total current flowing into a junction is equal to the total current leaving the junction<\/p>\n Young Julian:<\/strong> But, you just taught me about capacitors. They have current flowing into them, but not out the other side, right?<\/p>\n EE:<\/strong> Err… yeah, but only for a short time. It doesn’t really apply to capacitors.<\/p>\n YJ:<\/strong> Aren’t capacitors one of the basic components of electronics? How can a major rule not apply to them?<\/p>\n EE:<\/strong> You don’t understand yet. Let me try something easier.<\/p>\n Ohm’s Law says V=IR, voltage equals current multiplied by resistance.<\/p>\n YJ:<\/strong> Oh, so if I increase the resistance in this circuit, the voltage will increase!<\/p>\n EE:<\/strong> No, the voltage always stays constant. The current will reduce.<\/p>\n YJ:<\/strong> Huh? Why didn’t you say I = V\/R then? That way, the constants are on the right, and the unknown is on the left – you know, like they force us do in algebra all the time.<\/p>\n EE:<\/strong> Yeah, whatever. It’s the same thing. Nevermind, did you finish wiring the flashing LED circuit yet?<\/p>\n YJ:<\/strong> No, I think these LEDs you just gave me are dead. I am measuring the resistance – yes, in both directions – and it is infinite.<\/p>\n EE:<\/strong> Oh, that doesn’t prove anything. They have very high resistance at low-voltages, but it drops off as the voltage increases.<\/p>\n YJ:<\/strong> Huh? Didn’t you say V=IR?<\/p>\n EE:<\/strong> Yes, but Ohm’s Law only applies to Ohmic resistors.<\/p>\n YJ:<\/strong> What’s an Ohmic resistor?<\/p>\n EE:<\/strong> One in which the relationship V=IR holds.<\/p>\n YJ:<\/strong> Whoa! So Ohm’s Law is that V=IR, but only where it is true that V=IR? Isn’t that a tautology? You call it a Law of Physics, and it contains no information content!? <\/p>\n EE:<\/strong> Hmmm… Let me make it simpler for you. Electricity is like water flowing through a pipe…<\/p>\n YJ:<\/strong> Oh no, not this one again.<\/p>\n EE:<\/strong> …current represents the amount of water flowing through the pipe, and resistance is like an obstruction in the pipe, and voltage is the water pressure.<\/p>\n YJ:<\/strong> Right, so it is like when I play with the garden hose. If I put my finger over the end of the hose, the water will shoot out faster.<\/p>\n EE:<\/strong> No, no! The electricity doesn’t speed up or slow down.<\/p>\n YJ:<\/strong> What? So it’s nothing like water then. Well, what’s the equivalent of a capacitor in this analogy?<\/p>\n EE:<\/strong> Well, um, it’s like a swimming pool being filled up; the capacitance is like the size of the swimming pool<\/p>\n YJ:<\/strong> Is the water pipe filling the pool from the top or the bottom? <\/p>\n EE:<\/strong> What? At the bottom, I think.<\/p>\n YJ:<\/strong> Well, what happens when it overflows.<\/p>\n EE:<\/strong> Err.. I kind of empties all at once – err.. okay forget the swimming pool. Consider the analogy of a bucket, think of it like a bucket with a collapsible bottom.<\/p>\n YJ:<\/strong> Talk about an analogy that doesn’t hold water! Where’s the pipe? You fill buckets from the top.<\/p>\n EE:<\/strong> Umm.. er…<\/p>\n YJ:<\/strong> Can I play with my Commodore-64 now? Software makes so much more sense than this.<\/p>\n EE:<\/strong> Yes, go right ahead.<\/p>\n","protected":false},"excerpt":{"rendered":" There’s a very good reason why I am not a fully-qualified Electronics Engineer. 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