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.
The frequency is the number of vibrations in a second and is given the unit Hertz or Hz. High frequency sounds are usually shrill like a whistle whereas low frequency sounds are more like the deep hum of an amplified bass instrument. The highest frequency that most humans can hear is 20,000 cycles per second or 20,000 Hz. This limit gets lower as humans age. Older people generally donât have as large of a hearing range as younger people. The lowest frequency a human can hear is only 20 Hz, but we can feel sounds lower than that such as for an earthquake. Answer 3: