Interferometers figure prominently in the history of experimental physics. They were at the heart of the Michelson-Morley Experiment of 1887 that attempted unsuccessfully to detect the existence of an ether wind, a hypothetical medium for light transmission. (The null result was not because of any inadequacy in the instrumentation or deficiency in the design of […]
FAQ
Joseph Henry and mutual inductance
Joseph Henry (1797-1878) discovered the phenomenon of mutual inductance independently and more or less simultaneously with Michael Faraday. Because Faraday published his results a little earlier, he received credit for the discovery. But due to the large volume and quality of his published research, Henry gained stature early in life. He was six years younger […]
Basics of analog-to-digital converters
We straddle two realms, analog and digital. The output of a sensor, musical instrument, the human voice, and most of the signals that originate in the real world are analog. Today most information processing is digital. This works well in terms of audio and video quality, but analog data must be converted by an analog-to-digital converter (ADC) […]
Basics of quartz crystal oscillators
By David Herres Some materials acquire an electrical charge when they are compressed or otherwise dimensionally stressed. They are said to exhibit the piezoelectric effect. If the property is to be manifest on any but an atomic level, the material must be a crystal, with the atoms organized in a lattice. The piezoelectric effect was […]
ICs and timers
Moore’s law, actually more an observation than an edict, states that the number of transistors that can sit on a single semiconductor chip may be expected to double every two years. (Another version sets the time frame as 18 months.) The assertion is flawed because it suggests that before long the device population on a single chip […]
How much bandwidth?
The cost of an oscilloscope depends primarily on its bandwidth and, to a lesser degree, on added features such as an internal arbitrary function generator (AFG) and other options. If the price of the instrument is acceptable, the rational choice would be to go for the best device immediately. But in the real world most […]
Understanding the basics: What is characteristic impedance?
We speak of 50- or 75-Ω coaxial cable. The novice wonders if these numbers apply to a given length, say 100 ft. Could you connect an ohmmeter to one end of the cable and expect to get that reading with or without the conductors shunted at the far end? The answer is absolutely not. The characteristic impedance […]