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Science | Science Experiment of the Week 7 | 272 - Speed of Electricity

Does electricity really travel at the speed of light?



This Week's Experiment - #272 The Speed of Electricity

These experiments are from Robert Krampf - The Happy Scientist



This week's experiment is the result of a discussion that I recently had involving a common misconception about the speed of electricity. Many books say that electricity travels at the speed of light, but does it really? To find out, you will need:

a garden hose
a water faucet

First, lets take a look at this misconception. Turn on the light in the room where you are. After you flipped the switch, how long did it take before the light came on? It seems to happen instantly. When you flipped the switch, did the electricity rush past the switch, through the wires to the light, all at the speed of light?

No. Electricity is caused by the movement of tiny pieces of atoms called electrons. If you could see one of these electrons as it moves through the wire, you would find that it moves only a few centimeters per second. Now wait a minute! If the electricity is that slow, why doesn't it take several seconds for the light to come on?

To understand that, go outside and get your garden hose. Make sure that it is empty (no water in it) and connected to the faucet. Turn on the faucet and notice how long it takes before water squirts out the end of the hose. It probably took several seconds. OK that makes sense. It takes a while for the water to move through the hose to the end.

Next, turn off the water. Wait a second and then turn it back on. How long did it take this time for the water to squirt? It happened almost instantly! Was the water in the hose moving at the speed of light this time? No, of course not. What was different? The hose was already full of water. Water coming past the valve on the faucet pushed on the water already in the hose. All the water in the hose moved and some came out the other end as soon as you turned on the faucet.

The same idea applies to electricity. The wires in your house contain lots of electrons, just as the garden hose contained water. When you turn on the switch, the electrons in the wire get a shove and they all move, just as the water in the hose. Neither is moving at the speed of light, but both get instant results at the far end. Just be sure that the hose is not pointed towards anyone or you may have to move at "light speed" to get away.





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