Chap. 18
WAVES AND SOUND
WAVES:
are rhythmic disturbances that carry energy through
matter or space. They travel through a
medium.
MEDIUM:
is a material through which a wave transfers energy.
Examples: water waves use water, Earthquakes travel
through the Earth. Exceptions: are
radio and light waves.
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TYPES OF WAVES:
TRANSVERSE
WAVES:
the medium moves at right angles to the direction
the wave travels.
COMPRESSIONAL
WAVES:
matter vibrates in the same direction as the wave
travels.
Measuring
transverse waves:
Crests: highest point of the wave.
Troughs: lowest point of the wave.
Wavelength: is the distance between a
point on one wave and the identical point on the next wave. Can be from crest to crest or trough to
trough.
Amplitude: is the distance from the
crest or trough of a wave to the rest position of the medium.
Frequency: is the number of wave
crests that pass one place each second.
Expressed in hertz (Hz). One
hertz is equal to one wave per second.
WAVE VELOCITY:
velocity = wavelength x frequency
l = wavelength (Greek letter lambda).
v = l * f
Examples:
COMPRESSIONAL
WAVE:
Matter vibrates in the same direction as the wave
travels.
COMPRESSION:
The crowded area in the spring.
RAREFACTION:
The less dense area of the wave.
SPEED
OF A WAVE IN MEDIA:
Depends on
1. medium through which it
travels.
2. temperature of the medium.
Speed
of sound in air at: 20 oC is 344 m/s
0
oC is 332 m/s
PITCH:
is
the highness or lowness of a sound.
Pitch depends on frequency.
ULTRASONIC:
waves
are used in sonar as well as in medical diagnosis and treatment. Sonar (sound navigating ranging) is a method
using sound waves to estimate the size, shape, and depth of underwater objects.
INFRASONIC:
are
subsonic waves that have frequencies below 20 Hz. These are produced by heavy machinery and thunder.
INTENSITY:
of a
sound wave depends on the amount of energy in each wave. This is related to the amplitude of the
wave. This is measured in decibels
(dB), above 120 dB can cause permanent hearing loss.
LOUDNESS:
is
the human perception of sound intensity.
DOPPLER EFFECT:
A
change of wave frequency due to a moving
wave source.
MUSIC:
is
created using specific pitches and sound quality and by following a regular
pattern.
NOISE:
the
most common kind of sound. (who makes
the most noise?)
has
no definite _________ or ___________
RESONANCE:
of an object occurs when
sound reaches the object at the same natural frequency and thus causes the
object to vibrate.
SOUND QUALITY:
describes
the differences among sounds of the same
pitch and loudness.
INTERFERENCE:
is
the ability of two or more waves to combine
and form a new wave.
ACOUSTICS:
The
study of sound.
REVERBERATION:
the echoes
of sound in a hall (reflections of sound)
ELECTROMAGNETIC
WAVES:
are transverse waves produced by the motion of
electrically charged particles.
Examples: light, radio waves, TV, and microwaves
ELECTROMAGNETIC
RADIATION:
are electromagnetic waves.
RADIATION:
is the transfer of energy by electromagnetic waves.
PHOTONS:
are tiny, particle-like bundles of
radiation.
Einstein, in 1905, hypothesized that light was
composed of tiny particles.
RADIO
WAVES:
have long wavelengths and low frequencies. They, therefore, have the lowest photon
energy.
MICROWAVES:
radio waves with the highest frequency and energy.
INFRARED
RADIATION:
has a wavelength slightly longer than visible light.
Medical diagnosis: tumors are warmer than healthy tissue.
Infrared
photography: used to see where your house is losing heat.
Night
vision: detect infrared rays given off by the body.
Alarm
systems: used to detect objects that give off infrared radiation.
VISIBLE
RADIATION:
Light, is the only part of the electromagnetic
spectrum you can see?
ULTRAVIOLET
(UV) RADIATION
has a higher frequency than visible
light, so its photons are more energetic and have greater penetrating power
than photons of visible light. Exposure
to UV radiation enables the skin cells to produce vitamin D, which helps to
make healthy bones and teeth. It can
also be used to kill microorganisms in food and on hospital equipment. Too much exposure causes: sagging dry skin,
skin cancers, and killing of healthy cells.
OZONE
LAYER:
protects us from the UV radiation from the sun. It is a gaseous form of oxygen (O3).
DESTROYING
CELLS:
Gamma
Rays have the highest frequency and are the most penetrating of all the
electromagnetic waves. They are emitted
from the nuclei of radioactive atoms.
Treatment in cancer using gamma rays has been
widespread since the 1980’s.
OPAQUE
MATERIALS:
absorb or reflect all light.
Examples: heavy window curtains or
clay.
TRANSLUCENT
MATERIALS:
allows some light to pass through, but you cannot
clearly see objects through them.
Examples: frosted gall, shear curtains and waxed
paper.
TRANSPARENT
MATERIALS:
allow light to pass through and you can clearly see
objects through them.
Examples: glass and some water.
COLOR
AND LIGHT
PHOTORECEPTORS:
Rods:
is more sensitive to dim light. Useful
in night vision.
Cones:
Allow you to distinguish colors and detailed shapes of objects. Most useful in daytime vision. There are three kinds: Reds cones, red and
yellow; Green cones, yellow and green; Blue cones, blue and violet.
COLORBLINDNESS:
is a sex-linked trait that is more dominant in males
than in females.
PIGMENTS:
is a colored material that absorbs some colors and
reflects others.
INCANDESCENT
LIGHTING:
is produced by a thin wire called a
filament. +80% of energy is given off
as heat.
FLUORESCENT
LIGHTING:
filled with a gas, normally argon,
that is at a low pressure. Produces
light without excessive loss in thermal energy.
Wave
properties of light
REFLECTION:
occurs when a wave strikes an object
and bounces off.
Incident beam is the beam that strikes
the mirror.
Reflected beam is the beam that
bounces off the mirror.
LAW
OF REFLECTION:
states that the angle of incidence is
equal to the angle of reflection.
REFRACTION:
is the bending of waves caused by a
change in their speed when they move from one medium to another. Amount of refraction depends on:
1. the medium
2. the wavelength
DIFFRACTION:
is the bending of waves around a
barrier. Electromagnetic, sound and
water waves can all be diffracted. Examples?
PLANE
MIRROR:
one with a flat surface.
Example: a piece of glass. You appear upright and the same size.
VIRTUAL
IMAGE:
is an image in which no light rays
pass through the image. Formed from a
plane mirror. This image appears behind
the glass.
CONCAVE
MIRRORS:
if the surface of a mirror is curved
inward, like the inside of a spoon.
OPTICAL
AXIS: the straight line drawn through the center of the mirror.
FOCAL
POINT: light rays parallel to the optical axis are all reflected to pass through
one point on the optical axis.
FOCAL
LENGTH: the distance from the center of the mirror to the focal point.
REAL
IMAGE: an image that is enlarged and upside down, and because the light rays
meet the image.
CONVEX
MIRRORS:
type of mirror that curves
outward. The image is always virtual,
upright, and smaller than the actual object.
CONVEX
LENSES:
are thicker in the middle, amount of
refraction depends on the change in the speed of light as it passes through the
material, and shape of the object.
Convex lenses can produce real and virtual images, upright, inverted,
enlarged, or reduced. The type of image
formed depends on the position of the object and the focal length of the lens.
CONCAVE
LENSES:
Thinner in the middle and thicker at
the edges. The rays diverge and never
form a real image.
IMPROVING
THE VISION:
OPTICAL
INSTRUMENTS:
TELESCOPES:
REFLECTING TELESCOPES:
REFRACTING TELESCOPES:
MICROSCOPES:
CAMERAS:
POLARIZED
LIGHT:
LASERS:
COHERENT
LIGHT:
INCOHERENT
LIGHT:
OPTICAL
FIBERS: