Glossary of final test physics

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light –
Electromagnetic radiation that has a wavelength in the range from about 4,000 (violet) to about 7,700 (red) angstroms and may be perceived by the normal unaided human eye.
electromagnetic waves –
waves that do not require a medium to be transferred.
visible region –
the range of electromagnetic waves which stimulate the retina of our eyes. This region consists of a spectrum of wavelengths, which range from approximately 700 nanometers (abbreviated nm) to approximately 400 nm.
nanometer –
One billionth (10-9) of a meter.
quantum theory –
a theory in physics based on the concept of the subdivision of radiant energy into finite quanta and applied to numerous processes involving transference or transformation of energy in an atomic or molecular scale
light ray –
an imaginary line perpendicular to the wavefront.
smallest amount of energy that can be transfered in an electromagnetic wave.
umbra –
a region of complete shadow resulting from total obstruction of light
penumbra –
A partial shadow, as in an eclipse, between regions of complete shadow and complete illumination
luminous flux –
the part of the total radiant power emitted from a light source which affects the sense of sight.
luminous intensity (I)–
F/ Ω the luminous flux emitted per unit solid angle.
steradian –
A unit of measure equal to the solid angle subtended at the center of a sphere by an area on the surface of the sphere that is equal to the radius squared.
illumination (E)–
(= F/A)The luminous flux per unit area at any point on a surface exposed to incident light.
isotopic source
a light source that emits evenly in all directions.
reflection –
the phenomenon of a propagating wave (light or sound) being thrown back from a surface
refraction –
the change in direction of a propagating wave (light or sound) when passing from one medium to another
Mechanical wave –
a disturbance traveling through a material media transmitting energy from one point to another.
Transverse wave –
a wave in which the disturbance is at right angles with the direction of the wave travel.
Longitudinal wave –
a wave in which the disturbance is parallel to the velocity
Wavelength –
The distance between adjacent points of a similar phase.
wave speed –
wave length per period.
frequency –
The number of complete cycles per second of a complete waveform.
Linear mass density –
mass per unit length.
sound –
Vibrations transmitted through an elastic solid or a liquid or gas, with frequencies in the approximate range of 20 to 20,000 hertz, capable of being detected by human organs of hearing. Transmitted vibrations of any frequency.
resonance –
The increase in amplitude of oscillation of an electric or mechanical system exposed to a periodic force whose frequency is equal or very close to the natural undamped frequency of the system.
pitch –
the property of sound that varies with variation in the frequency of vibration
loudness –
Characterized by high volume and intensity
quality –
An inherent or distinguishing characteristic; a property, particularly the shape of the wave.
beats –
To cause a reference wave to combine with (a second wave) so that the frequency of the second wave can be studied through time variations in the amplitude of the combination.
intensity level –
loudness of the wave, the power transferred by the wave.
decibel –
A unit used to express relative difference in power or intensity, usually between two acoustic or electric signals, equal to ten times the common logarithm of the ratio of the two levels.
audible sound –
sound waves in the frequency range from 20 to 20,000 Hz.
infrasonic –
a frequency below the audibility range of the human ear (below 20 Hz).
ultrasonic –
acoustic frequencies above the range audible to the human ear, or above approximately 20,000 hertz.
hearing threshold –
the faintest audible sound (1x 10 -12 W/m² or 0 dB).
pain threshold –
the point at which sound intensity is intolerable to the ear (1W/m² or 120 dB).

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