How Everything Works
How Everything Works How Everything Works

Question 1190

What is the speed with which electric power is transmitted through the power grid? Believe it or not, the education center at an important nuclear power plant claims that "electrons travel at the speed of light," an obvious impossibility for current in a copper wire. What is the maximum speed of an electron in a commercial electric power grid? in a superconductor? — AW, Alexandria, VA
Amazingly enough, the speed at which electric power travels through a wire is very different from the speed at which electrons move through that wire. In most wires, electric power travels at very nearly the speed of light while the electrons themselves travel only millimeters per second! This statement is true whether the electricity is traveling in a copper wire or a superconductor!

To understand how this difference in speeds is possible, think about what happens when you turn on the water to a long hose. If that hose is already filled with water, water will immediately begin pouring out of the hose's end even though the water is flowing quite slowly through the hose. While the water itself moves slowly, the water's effects travel through the hose at the speed of sound in water—several miles per second! Water at the end of the hose "knows" that you have opened the faucet long before new water from the faucet arrives.

Similarly, when you turn on a flashlight, electrons begin to flow out of the battery's negative terminal at speeds of only a few millimeters per second. But these electrons don't have to travel all the way to the light bulb for the bulb to light up. When these electrons leave the battery, they push on the electrons in front of them, which push on the electrons in front of them, and so on. They produce an electromagnetic wave that rushes through the wire at an incredible speed. As a result, electrons begin flowing through the light bulb only a few billionths of a second after the first electron left the battery. So while the electrons that carry electricity through the power grid flow rather slowly, the power they deliver moves remarkably fast.


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