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Taking Measure

Just a Standard Blog

What’s in a Name? The Tesla

Header graphic featuring photo of Nikola Tesla, an MRI machine, and electricity
Credit: B. Hayes/NIST, Shutterstock

Do you enjoy flipping on the light switch or plugging in that favorite electrical device? Well, you can thank Nikola Tesla — born 167 years ago today — for that amazing invention. 

You may think of Thomas Edison as the main pioneer in electricity. But Nikola Tesla brought us alternating current (AC) electricity, which is the type of electricity that is widely used in our homes and buildings today. As the name implies, alternating current reverses direction at regular intervals, and it turns out that it’s much better for moving electric power over long distances. 

Drawing of Nikola Tesla with his chin propped on his hand.
Nikola Tesla
Credit: vkilikov/Shutterstock

This is different from direct current (DC) electricity, which is commonly used in batteries. While Edison did not invent DC, he did have patents on this type of electricity. Edison was a big proponent of DC power before Tesla demonstrated AC power’s advantages in 1893. This led to a feud between the two pioneers, known as the “War of the Currents.”

Like many early inventors and scientists, Tesla has a unit of measure named after him. 

The “tesla” is the unit for magnetic flux density. Think of magnetic flux density as a measure of magnetic strength. Imagine you are holding a sugar cube in your hand; it’s fairly light and not very dense. Now, imagine the cube turns into lead. It’s now heavy and quite dense. The tesla is a measure of that density, but for the strength of a magnetic field instead of the mass of an object.

That tesla is not just an abstract physics term; it’s actually used every day. 

One particularly important area is when it comes to MRI machines that are widely used in medicine. When you get an MRI, you’re placed in a large magnet. The tesla is a measure of the strength of that magnetic field that surrounds you in the machine. 

View through the top end of an MRI machine as a dark-haired patient lies inside.
The tesla is a measure of strength of the magnetic field that surrounds a patient when they’re in an MRI machine.
Credit: Orion Production/Shutterstock

A typical MRI machine has 1.5 to 3.0 teslas in strength. Experimental MRIs even go up to 10.5 teslas. The different types of MRI machines use varying amounts of teslas depending on the quality of images you need.

Besides the tesla, there’s a similar measurement for a related quantity known as magnetic flux, which measures the total magnetic field going through an object, as opposed to just its density. That’s called a “weber.” No, you can’t make these names up! The weber is named after Wilhelm Eduard Weber. Here’s how you say his name in case you were wondering. 

But today we’re here to remember Tesla’s contributions on his birthday, so we will save Mr. Weber for another day. 

About the author

Sandy Ressler

Sandy Ressler has been at NIST for nearly 40 years. (Yes, he’s old.) Following a short few years at Bell Labs, during which it was broken up (not due to Sandy’s work), Sandy has been doing computer graphics of various sorts at NIST. He is involved with 3D standards for the web and a variety of virtual reality technologies. He’s the co-author of the now classic Life with UNIX and the virtually unknown Art of Electronic Publishing. He holds an M.F.A. in visual arts (computer graphics), which continues to confuse management. In his off time, he loves to chase his grandkids.

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