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.
Instruments use resonance to amplify sound
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.
hammer - (also called the malleus) a tiny bone that passes
vibrations from the eardrum to the anvil.
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 model describes light as transverse waves that do
not require a medium to travel.
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 object. Light
wave can also interfere with one another to produce
standing waves.
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 light because
in bright light waves should have a greater amplitude.
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 energies,
frequencies, and wavelengths.
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.
The point where light hits the surface is called the
normal. The normal forms a perpendicular line to the
surface
Reflection and Color
Mirrors
Flat mirrors create virtual images.
an image that forms at a location from which light rays
appear to come but don 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 actually
come together at a specific location
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 wavelengths
and absorbs all other wavelengths.
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 magenta can
produce red, green, and blue. All three mixed together you
get black.
Reflection and Color
Black is the absence of collor
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 the
normal
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 air of
different temperatures, light will refract causing mirages.
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 refracted
twice. When it enters then again when it exits. However,
the light ray remains parallel to the original ray
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)
create only a virtual image
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 magnifying glass
and creates an even larger virtual image
Refracting telescopes work like microscopes
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.
Cones are responsible for color vision, but they only
respond to bright light
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 slowest and
red light travels the fastest.
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 different
frequencies into its individual component waves.
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.