It was 1923, and radio was the phenomenon of the day. Over 600 broadcast stations were on the air, and Americans bought 100,000 receivers that year. (Sales would jump to 1,500,000 in 1924.) Many owners hosted “radio parties” and danced to the latest jazz music with their friends. At the same time, the game of Bridge was sweeping the country. Read how one card company used this “new technology” to promote their products.
When the concept of electromagnetic waves was first proposed around 1864, it was met with great skepticism. As a result, the idea languished for a long time. It took several decades for a handful of dedicated persons — infatuated with the mysteries of electricity and magnetism — to finally put the theory on a solid footing.
In this article, we’ll take a look back at this period that launched the serious study of radio waves. We’ll examine the contribution of James Clerk Maxwell, the man most responsible for the concept. Next, we’ll look at the work of several notable scientists who came after Maxwell, and see how they confirmed the existence of radio waves.
This November, in Versailles, France, representatives from 57 countries are expected to make history. They will vote to dramatically transform the international system that underpins global science and trade. This single action will finally realize scientists’ 150 year dream of a measurement system based entirely on fundamental properties of nature. The International System of Units — informally known as the metric system — will change in a way that is more profound than anything since its establishment following the French Revolution.
Sometimes I wonder which of my portable digital voltmeters I can trust — the B&K, Fluke, or Amprobe. Usually, they’re pretty close but it bugs me not knowing whether they are right on the nose. Fortunately, these days, there are a number of very accurate voltage reference circuits that you can build or purchase for a few dollars.
In the US, the DC volt is legally defined by the Josephson array — a super conducting quantum device with a highly repeatable output voltage. Banks of standard cells and temperature-stabilized zener diode references are used by the National Institute of Science and Technology (NIST) to calibrate DC meters for scientific and industrial customers. So how is the AC volt defined?
How many times each day do you pick up a probe to measure a DC voltage? The meter reads, say 4.65 volts, and we usually accept it without question. But just what is a volt and how is it maintained? Here's a fascinating look at the search for increasingly more accurate methods of building a “standard volt.”