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Transmitted light
Transmitted light
Light that comes from a source, such as a light bulb (see: Electric light). Transmitted light has not been reflected from a surface. If it had, it would be called reflected light (see: Reflection).
Treble
The highest voice part in singing (see: Human voice) or the type of instrument with the highest range (for example, treble recorder).
Treble also refers to the upper half of the whole tonal range of an instrument or voice (the lower half being called bass). (See also: Alto; Bass; Tenor.)
Tuning fork
A U-shaped metal bar with a central stem. It is made to produce a particular musical pitch (frequency) and then used to help tune other musical instruments. Tuning forks do not go out of tune. They were invented in 1752 by John Shore.
A tuning fork produces a pure tone with no overtones. Thus, although it is useful for tuning other instruments, the tone from a tuning fork sounds uninteresting. (See also: Beat.)
 Tuning fork – The sound wave from a tuning fork consists of a fundamental only. There are no overtones. So, because the tuning fork vibrates with a single pitch, or frequency, the oscilloscope shows an even, simple curve.
Tweeter
A loudspeaker with a cone diameter of a few centimetres. It is designed to reproduce the highest sound frequencies.
Ultraviolet light
Light that is just beyond the purple end of visible light. Ultraviolet waves are slightly shorter than we can see.
UV
Ultrasound, ultrasonics
High-frequency sound waves. They are beyond the range of human hearing. They are made by applying a voltage to both sides of a quartz crystal. That makes the crystal expand. When the voltage is taken away, the crystal shrinks again. By using a cycle of electricity, a beam
of ultrasound can be produced. Ultrasound beams were first used to detect submarines. Later, they were used to map the ocean floor. The system came to be called sonar.
Ultrasonic beams can be used for many other purposes, such as removing plaque on teeth or to break up kidney stones.
Bats use ultrasound as a means of detecting their surroundings and to find food (insects) in the dark. Porpoises and whales also use ultrasound to detect shoals of fish.
Velocity of light
(See: Speed of light.) Virtual image
(See: Imaginary image.)
Vision
The ability to see. The eye is an instrument for gathering light and concentrating, or focusing, it on very sensitive cells at the back of the eye. There are two groups of these cells – cones for interpreting colour and brightness of light, in the centre of the eye, and rods that respond to low light levels but are less sensitive to colour around the edge of the eye.
Once the light has been received, it causes chemical changes in the cells, and that in turn releases a
tiny current of electricity that races along nerves to the brain, where it is interpreted as light.
Voice
(See: Human voice.) W
Watt
A unit of power. Named after
James Watt, an English engineer. Amplifiers and loudspeakers are rated in watts. A 200 watt (W) amplifier/loudspeaker system could produce a sound level in a room too loud for most people to tolerate. A low-power system, say 5W, would not have enough power to make the loudspeaker cone vibrate properly
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