You need two important things for an electric circuit: first you need a closed conductive path that goes from the positive to the negative terminal of the battery. When I teach this activity to kids, there’s always a couple that try to light up the LED just using the LED and wires (they forget about the battery completely!) You always need a power source in the circuit in order for charges to flow. The charges only flow through something that conducts electricity. Sometimes kids forget about the conductive part, and just try to touch the plastic coating on the wires to the LED and are frustrated when it doesn’t work right. It must be a closed conductive loop.
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The second thing is that there needs to be an electric potential difference across the two ends of the circuit. (You can think of the ends as the ends that are connected to the battery.) Because it takes energy to move the charge from a low to a high potential (remember how it takes energy to go up a flight of stairs?), there needs to be something that supplies the charges with the energy they need to go from a low to a high electric potential so then they can move through the circuit on their own. As the charge moves though the circuit, it loses energy until it reaches the negative terminal at zero energy. Then the battery gives that charge energy and it moves back up to the positive terminal at high energy and does it all over again. The battery pumps up the charges and creates an electric potential difference across the two ends of the circuit.
In your house, the electric outlet that you plug appliances and lamps into is the electric potential difference. The three holes in the outlet are hot, neutral, and ground.
The hot terminal is the smaller one on the upper right, and this has the highest potential. Neutral is the larger one on the upper left, and it is the return path for current (and should always be considered to be high potential. It’s unfortunately pretty common for hot and neutral wiring to be reversed, because the outlet still works if it is.) Ground is the roundish one at the bottom and is there for safety. Ground and neutral are connected together back at the box, and they give electricity the quickest and simplest way back to the low potential. An ungrounded device (including extension cords) can be dangerous if there’s no path to ground except through you.
The electrical outlet in US homes supplies 110-120 volts of voltage and 15-20 amps of current. On the other hand, a AA battery has 1.5 volts and about 50 mA (that;s 0.050 amps), depending on the type of battery and what kind of load you are putting on it.
And just in case you’re considering poking something into the outlet, over 4,000 people every year are in the emergency room for injuries that have to do with sticking something other than a plug into an electrical outlet, about one third of them are kids under 18 years old. And those are just the ones you made it to the hospital… some were not as lucky and never made it at all. The current can kill you because you’re made up mostly of water, which makes it a really good conductor of electricity. Electricity is always looking for the easiest way to ground, and though you is one of those ways and the amount of current that passes through you is enough to stop your heart and damage your cells. Bottom line: the only thing you should put into an outlet is a plug.
Click here to go to your next lesson on the water analogy!
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