Chapter 15: Sound and Light
Section 1: Sound
Section 2: The Nature of Light
Section 3: Reflection and Color
Section 4: Refraction, Lenses, and Prisms
Sound
Key Terms:
Sound Wave
Pitch
Infrasound
Ultrasound
Resonance
Sonar
Sound
Properties of Sound
Sound wave are longitudinal waves, in which
particles of air vibrate in the same direction the
wave travels. Sound waves have compressions and
rarefractions.
Sound waves may be produced differently, but in all
cases a vibrating object sets the medium around it
in motion.
Sound
The Speed of sound depends on the medium (pg 491 Table 1)
The speed of sound in a particular medium depends on how
well the particles can transmit the compressions and
rarefractions.
Sound waves travel faster in solids and liquids than through
gases.
However, some solids, such as rubber; dampen vibrations so
that sound does not travel well. (Soundproofing)
Sound
Loudness is determined by intensity
The loudness of a sound depends partly on the energy
contained in the sound wave.
Intensity describes the rate at which a sound wave
transmits energy though a given area of the medium.
It depends on the amplitude of the sound wave as
well as the distance from the source.
Sound
A sound with twice the intensity of another sound does
not seem twice as loud. For a sound to seem twice as
loud the intensity would have to be 10 times the
intensity of another sound.
Relative intensity is found by comparing the intensity of
a sound with the intensity of the quietest sound a
human can hear; the threshold of hearing. It is
measured in decibels (dB)
0 dB Threshold of Hearing
120 dB Threshold of Pain
Sound
Pitch is determined by frequency
The pitch of a sound is related to the frequency of
sound waves.
Higher-pitch = higher frequency (Shorter
Wavelengths)
Lower-pitch = lower frequency
(Longer
Wavelenghts)
Sound
Humans hear sound waves in a limited frequency
range.
Humans hear sound waves with a frequency
between 20 Hz and 20,000 Hz
Below 20 Hz is call infrasound
Above 20,000 Hz is called ultrasound
Sound
Musical Instruments
Musical instruments rely on standing waves
By changing the length of the standing wave the
frequency will change.
The primary standing wave has a wavelength that
is twice the length of the string or column. This
is the fundamental frequency
Sound
Harmonic give every instrument a unique sound
Harmonic is the fundamental frequency and a
certain whole-number multiples of that
frequency.
Every musical instrument has a characteristic
sound quality resulting from the mixture of
harmonics.
Sound
Resonance is a phenomenon that occurs when two
objects naturally vibrate at the same frequency
These two vibrations are the natural frequency an
instrument has plus a forced vibration.
Natural frequency depends on the shape, size,
mass, and material an object is make of.
Sound
Hearing and the Ear
The human ear is a very sensitive organ that senses
vibrations in the air, amplifies them, and then
transmits signals to the brain.
Vibrations pass through three regions of the ear
Outer, Middle, and Inner (pg 496 Figure 7)
Sound
Sound waves pass though the ear canal and strike
the eardrum, they cause the eardrum to vibrate.
These vibrations pass from the eardrum through
the three small bones of the middle ear
(hammer, anvil, and stirrup). When the vibrations
reach the stirrup, the stirrup strikes a membrane
at the opening of the inner ear, sending waves
through the cochlea.
Resonance occurs in the inner ear
Sound
The cochlea contains a long, flexible membrane
called the basilar membrane. Different parts
of the basilar membrane vibrate at different
natural frequencies.
A wave of a particular frequency cause only a
small portion of the basilar membrane to
vibrate.
Sound
anvil - (also called the incus) a tiny bone that
passes vibrations from the hammer to the
stirrup.
cochlea - a spiral-shaped, fluid-filled inner ear
structure; it is lined with cilia (tiny hairs) that
move when vibrated and cause a nerve impulse
to form.
eardrum - (also called the tympanic membrane) a
thin membrane that vibrates when sound waves
reach it.
Sound
nerves - these carry electro-chemical signals
from the inner ear (the cochlea) to the brain.
outer ear canal - the tube through which sound
travels to the eardrum.
stirrup - (also called the stapes) a tiny, U-shaped
bone that passes vibrations from the stirrup to
the cochlea. This is the smallest bone in the
human body (it is 0.25 to 0.33 cm long).
Sound
Sound
Ultrasound and Sonar
Sonar is used for underwater location
Sonar – Sound Navigation and Ranging – is a
system that uses acoustic signals and echo
returns to determine the location of objects or
to communicate.
Ultrasound is above 20,000 Hz
Sound
Ultrasound imaging is used in medicine
Echoes of very high frequency ultrasound waves,
between 1 million and 15 billion Hz are used
to produce computerized images called
sonograms
Some ultrasound waves are reflected at
boundaries
The Nature of Light
Key Terms
Photon
Intensity
Radar
The Nature of Light
Waves and Particles
Two models of Light
1. Waves
2. Steam of Particles
Light produces interference patterns like water
waves
The Nature of Light
1801 Thomas Young devised an experiment to
test the nature of light. He was able show that
light produces a striped pattern similar the
pattern caused by water waves.
Light can be modeled as a wave
Young concluded that light must consist of
waves.
The Nature of Light
Light waves consist of electric and magnetic
fields. Because of this they are called
electromagnetic waves.
We can describe transverse waves by amplitude,
wavelength, and frequency.
The wave model also explains why light may
reflect, refract, or diffract when it meets and
The Nature of Light
The wave model of light cannot explain some
observations
One example is when light strikes a piece of
metal electrons may fly off the metal’s
surface.
According to the wave model, very bright red
light should have more energy then dim blue
The Nature of Light
Light can be modeled as a stream of particles
Energy from light is contained in small packets. A
packet of blue light carries more energy than a
packet of red light.
In the particle model of light, these packets are
called photons, and a beam of light is considered t
be a stream of photons.
The Nature of Light
Photons do not have mass; they are more like little
bundles of energy.
The model of light used depends on the situation
The energy of light is proportional to frequency
Higher the frequency more energy
Lower the frequency less energy
The Nature of Light
The speed of light depends on the medium (pg
501 Table 2)
In a vacuum, all light travels at the same speed,
called the speed of light 3 x 108 m/s (186,000
mi/s). Light is the fastest signal in the universe.
When light travels through a medium its speed
slows down.
The Nature of Light
The brightness of light depends on intensity
Intensity is the rate at which energy flows
through a given area of space.
Like the intensity of sound, the intensity of light
source decreases as the light spreads out in
spherical wave fronts.
The Nature of Light
The Electromagnetic Spectrum
We can detect light from 400nm (violet) to
700nm (red)
This is the visible spectrum and only makes up a
small part of the electromagnetic spectrum
The spectrum consists of light at al possible
The Nature of Light
Many modern tools take advantage of the
different properties of electromagnetic waves.
(Radar guns to cancer treatment)
Sunlight contains ultraviolet light (UV)
UV light has higher energy and shorter
wavelengths than visible light.
The Nature of Light
X rays and gamma rays are used in medicine
X rays have wavelengths less than 10-8 m and
gamma rays have wavelengths as short as 10-14
m.
Because both x rays and gamma rays have very
high energies, they may kill living cells or turn
them into cancer cells.
The Nature of Light
Infrared light can be felt as warmth (IR)
Microwaves are used in cooking and
communication
Microwave ovens use waves with a frequency of
2450 MHz (12.2 cm wavelenght).
The Nature of Light
Radio waves are used in communications and
radar
Radar – Radio Detection and Ranging – a system
that uses reflected radio waves to determine
the velocity and location of objects.
Reflection and Color
Reflection of Light
A light ray is an imaginary line running in the
direction that the light travels.
Rough surfaces reflect light in many directions
The reflection of light off a rough surface is
called diffused reflection
Reflection and Color
Smooth surfaces reflect light rays in one
direction
The reflected light is reflected off a surface at
the same angle that the incoming light struck
the surface.
Law of Reflection
The angle of incidence equals the angle of
Reflection and Color
Mirrors
Flat mirrors create virtual images.
an image that forms at a location from which light
rays appear to come but do not actually come.
Behind the mirror.
Curved mirrors can distort images
Reflection and Color
Because the surface of a curved mirror is not flat,
the line perpendicular to the mirror (the normal)
points in many directions.
Mirrors that bulge out are convex mirrors
Mirrors that are indented are concave mirrors.
Concave mirrors can create real images
an image of an object formed by light rays that
Reflection and Color
With a real image, light rays really exist a the
point where the image appears; a virtual
image appears to exist in a certain place, put
there are no light rays there.
Telescopes use curved surfaces to focus light
Reflection and Color
Seeing Color
Objects have color because they reflect certain
wavelengths
The color that we see is the color that the object
reflects.
If an object appears green it reflects green
Reflection and Color
If an object is place under light without the color it
reflects, it will appear black.
Colors may add or subtract to produce other colors
Additive primary colors red, green and blue can
produce the secondary colors of yellow, cyan, and
magenta. All three mixed together you get white
Subtractive primary colors yellow, cyan, and
Reflection and Color
Black is the absence of color
Refraction, Lenses, and Prisms
Refraction of Light
Light waves bend as they pass from one medium to
another. It bends because the speed of light is
different in each medium.
Higher Speed to Lower Speed rays bend toward the
normal
Lower Speed to Higher Speed rays bend away from
Refraction, Lenses, and Prisms
Refraction makes objects appear to be in different
positions.
The misplaced image of the object are virtual
images.
Refraction in the atmosphere creates mirages
Because light travels at slightly different speeds in
Refraction, Lenses, and Prisms
Light can be reflected at the boundary between
two transparent mediums
In order for this to occur, the angle at which light
rays meet the boundary have to be at the
correct angle.
This angle is the called the critical angle. This
type of reflection is called total internal
reflection.
Refraction, Lenses, and Prisms
Fiber optics use total internal reflection
Because fiber-optic cables can carry many
different frequencies at once, they transmit
computer data or signals for telephone calls
more efficiently than standard metal wires.
Refraction, Lenses, and Prisms
Lenses
A lens is a transparent object that refracts light
waves such that they converge or diverge to
create an image.
Lenses rely on refractions
Light traveling through a flat piece of glass is
Refraction, Lenses, and Prisms
When light passes through a curved lens, the
direction of the light changes.
Converging lens bends light inward (Convex)
create either a real or virtual image
depending
on the distance from the lens to the object
Diverging lens bends light outward (Concave)
Refraction, Lenses, and Prisms
Lenses can magnify images
Magnifying glasses are an example of a converging
lens
Microscopes and refracting telescopes use multiple
lenses
Microscopes use an objective lens first to form a
larger real images and the eyepiece lens acts as a
Refraction, Lenses, and Prisms
The eye depends on refraction and lenses
The cornea and lens refract light onto the retina at
the back of the eye.
The retina contains rods and cones.
Rods are more sensitive to dim light, but cannot
resolve details very well.
Refraction, Lenses, and Prisms
Dispersion and Prisms
Prism a system that contains two or more plane
surfaces of a transparent solid at an angle with
each other.
Different colors of light are refracted differently
In the visible spectrum, violet light travels the
Refraction, Lenses, and Prisms
Because violet light travels slower than red light,
violet light refracts more than red light when it
passes from one medium to another.
When white light passes through a prism, violet
light bends the most and red light the least with
the remaining visible colors in between.
Dispersion is the process of separating a wave of
Refraction, Lenses, and Prisms
Rainbow are caused by dispersion and internal
reflection
Sunlight is dispersed and internally reflected by
water droplets to form a rainbow.
Red light comes from droplets higher in the air
and violet light comes from lower droplets.