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Every note played on a musical instrument consists of a fundamental tone plus many harmonics. It is called a musical tone.
Hearing
The capture of sound by a sensitive part of the skin (in the case of humans by the ear). All arthropods (insects, spiders, crabs and so on) and vertebrates (mammals, fish and so on) can hear, although they each have a different hearing range and hear best in different mediums. For example, humans hear best in air, while fish hear best in water.
Some living things, such as insects, spiders and fish, can sense the speed of the vibration. Most others sense sound by the pressure of the sound on a sensitive piece of skin (in the case of humans the ear-drum).
Insects mainly hear through sensitive regions on the middle part (thorax) of their bodies. Mosquitoes hear through their antennae; cockroaches and similar insects hear through their abdomen in the range of 100 to 3,000Hz.
Insects may have one or two places that are sensitive to sound. All vertebrates have two ears, which enable them to sense not only the nature of the sound but also its direction. Bats use an echo- locating system, sending out high- frequency sound waves and then listening to the reflected waves to judge the position of objects in their path.
The ears of mammals are more complex than in other vertebrates and include an outer ear, which acts like a funnel, collecting sound and feeding it down to the ear- drum. Humans can hear sounds
at frequencies ranging from 15Hz to 15,000Hz, and children can hear sounds as high as 20,000Hz.
Sounds below 15Hz are called infrasound, and those higher than 20,000Hz are called ultrasound. Humans cannot hear them, but some birds, bats and insects use ultrasound. Dogs can also hear ultrasound and dog whistles normally use ultrasound. Dog whistles are normally also given an audible whistle, otherwise the owners do not know the whistle is working.
Hertz (Hz)
The unit of frequency. It is equal to the number of wave crests that pass a fixed point each second.
The number of hertz is therefore equal to the number of complete wave cycles per second. In sound the larger the number of hertz,
the higher the sound. In light, colours closer to the red end of
the spectrum have a larger number of hertz.
The unit is named after the 19th-century German physicist Heinrich Hertz.
Hi-fi
Short for high-fidelity, meaning good-quality sound. To be hi-fi, equipment must be able to cover 20 to 20,000Hz, and preferably 15 to 20,000Hz. The lowest notes on organs and pianos are 16.4 and 24.5Hz respectively. (See also: Dropout.)
Hue
The ‘colour’ property of a colour, such as red, yellow, green or blue.
Human voice
Humans make sounds by using air escaping from their lungs. The sounds we make are produced in a variety of ways. For example, vowels are produced when the vocal chords chop the air stream from the lungs into short bursts of
air. The rate of chopping controls the pitch of the voice. It is as low as 100 pulses per second for males, 200 pulses per second for females, and more for children.
The windpipe amplifies the voice. While the vocal chords act like a reed, the windpipe acts like a pipe, giving the sound its quality and amplification.
The sounds of speech are controlled by the way we hold our tongue, lips and palate.
Some sounds, such as the consonants b, d, f and others, do not involve the vocal chords; the sound is simply the air being blown from the lungs, combined with
the movement of tongue, lips and palate. With other speech sounds, such as n, the air is allowed to come out of the nose. (See also: Alto; Bass; Tenor; Treble.)
I
Imaginary image
The image that you see when you look into a mirror or through eyeglasses. This image cannot be seen on a screen or made into a photograph. The term virtual image is also used. An imaginary image
is produced when you are close
to a lens (see: Concave lens). The image is always upright. That is why we can see an enlarged upright image through eyeglasses.
Incandescence, incandescent light
The light produced when something glows. The effect is most commonly used in an ordinary light bulb, which are formally called incandescent light bulbs (see: Electric light). Electricity flowing through the filament makes the filament glow, or incandesce, white hot.
Incandescence, incandescent light
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