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What Is the Magnetic Constant, and Why Does It Matter?
This persnickety number determines the strength of magnetic fields. It figures in everything from motors and generators to audio speakers. Oh, and without it we’d live in eternal darkness.
It’s also how audio speakers create sound: An electric signal vibrates a magnetic driver, which generates pressure waves in the air. A simple version of this has two parallel wires carrying electric current ( I) in opposite directions, as shown in the diagram below. As they move away, the magnetic force decreases and the horizontal component of the tension in the support string increases (because of the change in angle).
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