thermionic emission (thurÂ´mÄ«onik imishÂ´Én), n the release of electrons when a material is heated (e.g., electron emission when the tungsten cathode filament of a radiographic tube is heated to incandescence by means of its low-voltage heating circuit).
The number of cycles per second (Hertz) (abbreviated as, hz) of anything that oscillates is called the frequency. The electricity of an AC wall outlet is said to have a frequency of 60 Hertz as it cycles negative then positive 60 times each second. Sound is an oscillating wave, but it has a broad range of frequencies. A low frequency sound (say, 50 hz) might sound like a low rumble, while a high frequency sound (say 12,000 hz), might sound more like a sizzle. A person with normal hearing can hear all the way up to about 20,000 hz.
Angular Frequency. Angular frequency, f, is defined as the number of circular revolutions in a given time interval. It is commonly measured in units of Hertz (Hz), where 1 Hz = 1 s â1. For example, the second hand on a clock completes one revolution every 60 seconds and therefore has an angular frequency of 1 / 60 Hz. = 1/f. Since we know that the frequency of the second hand is 1 / 60 Hz, we can quickly see that the period of the second hand is 60 s. It takes 60 seconds for the second hand to complete a revolution, so the period of the second hand is 60 seconds.