Chapter 16 Sound and Light
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Transcript of Chapter 16 Sound and Light
Chapter 16 Sound and Light Sound Sound wave: a longitudinal wave
that is caused by vibrations and that travels through a material
medium A series of compressions and rarefactions Carries energy
through medium All sound waves are made by vibrating objects that
cause the surrounding medium to move Sound Sound The speed of sound
depends on the medium
Depends on the temperature and the material through which the wave
travels Colder temperatures: slower Warmer temperatures: faster Gas
(air):slower (346 m/s) Liquids: faster than gas Solids: faster than
liquids Some solids like rubber, dampen vibrations so that sound
does not travel well (materials like rubber are used for
soundproofing) Sound Speed depends on the temperature and the
material through which the wave travels Sound Sound Sound Sound
Loudness is determined by Intensity
Intensity depends on the amplitude of the sound wave and your
distance from the source of the sound Greater the intensity, the
louder the sound Humans perceive loudness on a logarithmic scale A
sound seems twice as loud when its intensity is 10 times the
intensity of another sound Intensity is measured in units called
decibels (dB) An increase in intensity of 10 dB means a sound seems
about twice as loud Sound Sound Sound The quietest sound a human
can hear is 0 dB
A sound of 120 dB is at the threshold of pain Above this value
could cause permanent deafness Sound Sound Pitch is determined by
frequency
Pitch is a measure of how high or low a sound is and depends on the
sound waves frequency A high-pitch sound is made by something
vibrating rapidly (high frequency) A low-pitch sound is made by
something vibrating slowly (low frequency) Sound Sound Sound Sound
Humans hear sound waves in a limited frequency range
Frequency of 20Hz to 20,000Hz Frequency below the range of human
hearing is infrasound Frequency above the range of human hearing is
ultrasound Sound Sound Musical instruments: produce sound through
the vibration of strings, air columns, or membranes Strings: when
you pluck the string on a guitar, particles in the string vibrate.
Sound travels out to the ends of the string and then reflect back
toward the middle thus causing a standing wave on the string The
two ends of the string are called nodes, and the middle of the
string is called an antinode Standing wave exist only at certain
wavelengths on a string: fundamental frequency Primary standing
wave on a vibrating has a wavelength that is twice the length of
the string Sound Sound You can change the pitch by placing your
finger on the string anywhere on the guitars neck A shorter length
of string vibrates more rapidly, and the standing wave has a higher
frequency with a resulting higher pitch Sound All musical
instrument produce standing waves
Drum: standing waves formed on the membranes vibrate Wind
instruments: standing waves form in the column of air Opening and
closing holes changes the length of the air columns, which change
the wavelength and frequency of the standing waves Sound
Instruments Instruments use resonance to amplify sound
when one object vibrating at the same natural frequency of a second
object forces that second object into vibrational motion. String
and guitar body are vibrating at the same frequency Amplifies the
sound Electric guitars do not resonate well and must be amplified
electronically Sound Sound The human ear is a sensitive organ that
senses vibrations in the air, amplifies them, and then transmits
signals to the brain Sound waves travel through the outer ear
(auditory canal) and cause the eardrum to vibrate The vibration
passes from the eardrum through the three small bones of the middle
ear (hammer, anvil, stirrup) Stirrup vibrates the membrane of the
inner ear (oval window)sending the wavelength through the
spiral-shaped cochlea The cochlea contains a long, flexible
membrane called the basilar membrane Different parts of the
membrane vibrate at different frequencies Hair cells stimulate
nerve fibers sending impulses to the brain Sound Reflected sound
waves are used to determine distances and to create images
Ultrasound travel through most materials and some are reflected
when they pass from one type of material into another Sonar (sound
navigation and ranging)is a system used to locate objects
underwater Sound Sound The Nature of Light Waves and Particles: it
is difficult to describe all the properties of light with a single
model The two most common models describe light as a wave or as a
stream of particles The Nature of Light Light produces interference
patterns as water waves do The Nature of Light The model of light
as a wave is still used today to explain many of the basic
properties of light and lights behavior Transverse waves that do
not require a medium in which to travel Transverse waves described
by their amplitude, wavelength, and frequency Light waves are also
called electromagnetic waves because they consist of changing
electric and magnetic fields The Nature of Light The particle model
of light can explain some effects that the wave model cannot
explain Red light cannot knock electrons off the metal plate Blue
light can knock electrons off the metal plate The wave model of
light cannot explain this phenomenon The Nature of Light In the
particle model of light beam of light is a packet of particles
(photons) Not like ordinary matter No mass They are little bundles
of energy The Nature of Light The model of light used depends on
the situation
Wave model: can explain interference Particle model: explains how
light can travel across empty space without a medium The Nature of
Light The energy of light is proportional to frequency of the
electromagnetic wave The Nature of Light The speed of light depends
on the medium
Resented by the symbol: c 3 x 108m/s ( about 186,000 mi/s) When
light passes through a medium, such as air, water, and glass, it
travels slower than it does in a vacuum The Nature of Light The
brightness of light depends on intensity
Intensity depends on the number of photons per second, or power,
that pass through a certain area of space Decreases as distance
from the light source increases The Nature of Light Electromagnetic
Spectrum: consists of waves at all possible energies, frequencies,
and wavelengths The Nature of Light Radio waves: TV, AM/FM radio,
radar
Microwaves: cell phones, ovens Infrared: heat lamps Ultraviolet:
sunburn, insect vision X-rays. Gamma rays: medical functions The
Nature of Light Reflection and Color Every object reflectssome
light and absorbs some light It is useful to another model for
light, the light ray, to describe reflection, refraction, and many
other ways light behaves A light ray is an imaginary line running
in the direction that the light travels or path of photons
Reflection and Color Reflection of Light:
Rough surfaces reflect light rays in many directions Smooth
surfaces reflect light rays in one direction Law of reflection:The
angle of the light rays reflecting off the surface, called the
angle of reflection, is the same as the angle of the light rays
striking the surface, called the angle of incidence Both of these
angles are measured from a line that is perpendicular to the
surface at the point where the light hits the surface (normal)
Reflection and Color Reflection and Color Reflection and Color
Reflection and Color Reflection and Color Mirrors reflect light as
described by the law of reflection, and this light reaches your
eyes. The type of image you perceive depends on the type of mirror
Virtual image: an image from which light rays appear to diverge,
even though they are not actually focused there Cannot be projected
on a screen Real image: an image that is formed by the intersection
of light rays Can be projected on a screen Reflection and Color
Most mirrors are made by coating a piece of glass with a layer of
metal. The glass provides the smooth surface necessary for good
reflection and protects the metal from becoming scratched and
tarnished. Polished plate glass is used for the finest mirrors. A
solution containing silver nitrate is poured onto the glass, and a
deposit of silver adheres to the glass. The remains of the solution
are poured off and the glass is dried. The silvered surface (the
back of the mirror) is then coated with a protective substance,
such as shellac, to keep the silver from being rubbed off or
scratched. Reflection and Color Reflection and Color Curved
mirrors: imagines created are distorted Reflection and Color
Convex: bulge out Images smaller
Passenger side mirror Reflection and Color Convenience store
mirrors are convex. Convex mirrors will produce upright virtual
images that are smaller than the object. Their benefit is that they
allow you to see more area in the reflection. Reflection and Color
Concave: indented Images larger Reflection and Color Make up
mirrors are concave. Concave mirrors will produce upright,
magnified virtual images if the object is between the focal point
and the mirror. Reflection and Color Seeing colors: the colors that
you perceive depend on the wavelengths of visible light that reach
your eyes Objects have the color of the wavelength they reflect
Example: Green leaf reflects green wavelength and absorbs the other
wavelengths White: reflects all wavelengths Black: absorbs all
wavelengths Reflection and Color Reflection and Color Reflection
and Color Mixture of colors produce other colors
Additive Primary Colors: red, green, and blue Mixing light of two
of these colors produces the secondary colors yellow, cyan, and
magenta Mixing light of the three primary colors produces white
light Reflection and Color Reflection and Color Because filters and
pigments absorb light, the opposite effect happens when they are
mixed. The Subtractive Primary Colors-yellow, cyan, and magenta-can
be combined to create red, green, and blue If filters or pigments
of all three colors are combined in equal proportions, all visible
light is absorbed No light gets to your eyes, so you see black
Black is not a color, it is the absence of color Reflection and
Color Refraction, Lenses, and Prisms
Light waves bend, or refract, when they pass from one transparent
medium to another Refraction, Lenses, and Prisms
When light moves from a material in which its speed is high to a
material in which its speed is lower, such as from air to a glass
the ray is bent toward the normal Refraction, Lenses, and
Prisms
If light moves from a material in which its speed is low to one in
which its speed is higher, the ray is bent away from the normal
Refraction, Lenses, and Prisms
Refraction makes objects appear to be in different positions
Refraction, Lenses, and Prisms Refraction, Lenses, and Prisms
Refraction, Lenses, and Prisms Refraction, Lenses, and Prisms
A mirage is a virtual image that is caused by refraction of light
in the atmosphere The air temperature affects the speed at which
light travels. When light from the sky passes into the layer of hot
air just above the asphalt on a road, the light refracts and bends
upward away from the road. This refraction creates a virtual image
of the sky coming from the direction of the road. Your mind
visualizes water. Refraction, Lenses, and Prisms Refraction,
Lenses, and Prisms Refraction, Lenses, and Prisms
Lenses: when light passes through a medium that has a curved
surface, a lens, the light rays change direction. Refraction,
Lenses, and Prisms
Convex lens: converging lens When light rays pass through a lens
that is thicker in the middle, the rays are bent inward Refraction,
Lenses, and Prisms
Concave lens: diverging lens When light rays pass through a lens
that is thicker at the ends, the rays are bent outward Refraction,
Lenses, and Prisms
Microscope use a series of convex lens to magnify the specimen
Image Refraction, Lenses, and Prisms
Human eye depends on refraction and lenses Refraction, Lenses, and
Prisms Refraction, Lenses, and Prisms
Prism: separates white light into its component colors Air droplets
in the air can also separate the color in white light to produce a
rainbow Refraction, Lenses, and Prisms
Different colors of light are refracted by different amounts Light
waves travel at 3.0 x 108 m/s in a vacuum When a light wave travels
through a medium, the speed of the light waves depends on the light
waves wavelength Violet waves have a shorter wavelength and travel
slowest Red waves have a longer wavelength and travel the fastest
Because violet light travels slower than red light, violet light
bends more than red light when it passes from one medium to another
This effect is called dispersion Refraction, Lenses, and
Prisms
Rainbows are caused by dispersion and reflection