Circuits 101 – Power Flow

Think you’ve never created an electrical circuit before? I bet you’re wrong.

You know how you touch both terminals of a 9-volt battery to your tongue to make sure it works? That’s a circuit. The tingly zap you feel is the electricity flowing from the negative side of the battery, over your tongue, to the positive side. It doesn’t work when you just touch one of the terminals to your tongue, does it?

An electrical circuit is any controlled flow of electricity that creates a full loop. Your tongue, acting as a slimy conductor, connects both the positive and negative ends of the battery, so the power can make a full loop. Because there’s a path for the power to travel from the negative terminal to the positive terminal (again, via your tongue), the power flows. If there wasn’t a path, the power wouldn’t flow. That’s all a circuit is. More after the jump.

The classic classroom example of a functioning circuit is to wire a battery to a light bulb. By connecting both the positive and negative ends of the battery to the bulb, power can flow from the negative side of the battery, through the light bulb, and back around to the positive side to create a loop (what’s another word for loop? circuit?).

As the above graphic shows, power can only flow if there is a clear path from negative to positive. Even if you connect the light bulb to one of the power terminals, the bulb wont shine unless power can move through it, not to it.

Simple enough, though this popular demonstration doesn’t really demonstrate the direction of power flow. Based on the generic concepts of positive and negative, it’s easy to assume that power flows from the positive and returns to the negative. This isn’t the case, though, and to demonstrate that I like to use a slightly modified light bulb example:

LED (light emitting diode) bulbs are the tiny, low-power lights you find on most gadgets as power indicators. Unlike regular (incandescent) light bulbs which will usually light up even if it’s getting too much or too little power, LEDs have a very specific window of tolerance for voltage and amperage so your power source must be shunted with a tiny component called a resistor before it hits the LED or the bulb will sizzle, fry, and possibly pop right in your face. Because the power has to go through the resistor before it reaches the LED, it’s important to understand which direction the juice flows. If you put the resistor between the battery and LED on the positive side, the electricity will flow unresisted to the LED from the negative side and fry the bulb.

There you have it, now you know what a circuit is, how to create one, and what direction the power flows. You officially know more than the average first grader.

If you want to put this knowledge into use, you should check out my Mini LED Flashlight kit over at The Electroids Co. — it’s a great, simple kit with parts and instructions to help you build a neat little LED flashlight in an Altoids tin. Don’t forget, every order is an entry to win an iPod.