Science universe: Physics articles

headphone The term headphone is used here to include almost any device that fits into or over the ear for the purpose of sound reproduction. ( Hearing aids are not included.) Because headphones are used in pairs, the term is usually pluralized. The term phones is fairly common as a colloquial diminution of headphones but is not used here. An earphone used to be a single sound reproduction device designed for insertion into the ear, but has become rare. Pairs of earbuds are now common. Because this encyclopedia assigns more emphasis to electronic components than to consumer products, this entry provides only a superficial overview of fully assembled headphones, and deals more with the drivers inside them, their principles of operation, and the general topic of sound reproduction. What It Does A headphone converts fluctuations of an electric signal into pressure waves that the human ear perceives as sound. It can be used for reproduction of music for entertainment purposes, o...

audio indicator An audio indicator is defined here as a noise-creation device that generates a simple tone or series of tones. Unlike a transducer , which requires an external source of AC to determine its audio frequency, an indicator contains its own electronics and requires only a DC power supply. Either of these components is often described as a beeper or buzzer . While piezoelectric alerts formerly used crystals, only the more modern piezoelectric type that uses a ceramic wafer will be considered here. What It Does When DC power is applied to an audio indicator , in its simplest form it creates a continuous or intermittent tone of a fixed frequency. This is called an alert . Audio alerts are used in microwave ovens, washer/dryers, automobiles, gasoline pumps, security devices, toys, phones, and many other consumer products. They are often applied with touch pads, to provide audio confirmation that a tactile switch has been pressed. A few indicators are programmed to c...

transducer The term transducer is used here to describe a noise-creating device that is driven by external electronics. By comparison, an audio indicator (discussed in the next entry) contains its own internal electronics and only requires a DC power supply. Either of these components is often described as a beeper or buzzer . A speaker , more properly termed a loudspeaker , is an electromagnetic transducer but is seldom described in those terms. It has a separate entry in this encyclopedia and is defined here as a sound reproduction device that is larger and more powerful than a typical transducer and has a more linear frequency response. While piezoelectric transducers formerly used crystals, only the more modern piezo- electric type that uses a ceramic wafer will be considered here. Some transducers convert sound into electricity, but these are categorized as sensors , and will be discussed in Volume 3. The only transducers discussed in this entry are those that convert elec...

electroluminescence The field of electroluminescent devices is sometimes referred to as EL . The same acronym can also be applied as an adjective to an individual electroluminescent device, as in, for example, “an EL panel.” An organic light-emitting diode , more commonly known by its acronym OLED , is included in this entry because it is technically an electroluminescent device and its design concept is similar to that of an electroluminescent panel. Generic LEDs are also technically electroluminescent, but are not commonly described as such, and have their own entries in this encyclopedia under the subject categories LED indicator , LED area lighting , and LED display . What It Does An electroluminescent device configured as a panel , ribbon , or r ope-light contains phosphors that emit light in response to a flow of electricity. Panels can be used as backlights for LCD displays or, more often, as always-on low-power devices such as exit signs and night lights. Ribbons and ...