Transcript Chapter 4 PPT

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Chapter 4
Sound &
Light
Sound
Sound travels from one place to
another as sound waves
A sound wave is a
longitudinal wave that can only travel
through matter (Solids, liquids, gases)
Vibrations produce sound waves by
moving molecules in air.
How does the ear work?
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Sound waves are sent.
The outer ear “catches the sound waves”.
The middle ear takes the sound waves and “vibrates”
the eardrum.
The inner ear sends the messages to the brain.
Middle Ear
Outer Ear
Sound Waves

Inner Ear
The brain puts it together and hooray! You hear your
favorite song on the radio.
How sound waves travel!
Outer ear – Middle ear – Inner ear –
Catches
Vibrates
Sends
sound
Ear
Message
waves
Drum
To
Brain
 Sound waves are made up of two
parts:
1. Rarefactions
2. Compressions
 The tuning fork causes molecules
in the air to
move closer and then farther apart
 Like other waves, a sound wave can be
described by its: 1. Wavelength
2. Frequency
Wavelength: distance from center of
rarefaction to next rarefaction (vice versa)
Frequency: The # of wavelengths that pass
a given point in one second
The unit for
frequency is
Hertz (Hz)
Speeds of Sound Waves
 A sound wave’s speed increases when
the material’s density increases.
Solids and liquids are more dense
than gases.
Sound waves usually travel faster in
solids than in liquids or gases.
The speed of sound waves increase
as the temperature increases.
If sound travels faster in water than in
air…then why is it harder to talk to
someone underwater?
• Sound couples poorly moving from air to
water.
• Your lungs provide the burst of air when
talking underwater.
• In order for someone underwater to hear you,
the sound waves have to go from the air in
your mouth to the water surrounding you.
• This causes the sound waves to get reflected
where the air meets the water.
Pitch
 Pitch: how high or low a sound seems
A sound wave with a higher
frequency has a higher pitch.
A sound wave with a lower
frequency has a lower pitch.
Loudness
Loudness is the human sensation of
how much energy a sound wave
carries
A shout carries more energy than a
whisper.
The energy that the wave carries
relates to its amplitude.
Loudness (cont’d)
The more energy a wave has the
greater the amplitude.
A decibel scale is one way to
compare the loudness of sounds
Echo
An echo is a reflected sound wave.
Some animals use
echolocation
to locate
their prey and detect
objects.
Animals such as
dolphins and bats send
out sound waves and
when those waves hit
an object it bounces
back vibrations.
Sound Travels Through Matter
Liquids
Gases
Most of the sounds
we hear travel
through gases, such
as air.
Sound waves travel
slowly through the
air.
For example: Sound
from a bell, a horn,
or an alarm clock
travels through the
air.
Some sounds that
we hear travel
through water.
Sound waves travel
faster through
water than through
the air.
Sonar is the way to
use sounds to locate
objects under
water.
Solids
Some sounds that
we hear travel
through solids.
Sound waves travel
very fast through
solids.
For example: When
you hit a drum, it
vibrates, then the
sound travels
through the air, to
your ears.
Ultrasound
• Ultrasound scanners convert high-frequency
sound waves to images of internal body parts.
• The sound waves reflect from structures
within the body.
• The scanner analyzed the reflected waves and
produces images called sonograms.
Breaking the Sound Barrier
• When the vehicle (jet) exceeds the speed at
which sound travels.
• The cone of vapor you see is the existing
moisture in the air being condensed by
pressure wave created by the vehicle creating
a cloud.
Lesson 2: Light
Light
Light is a type of wave called an
electromagnetic wave.
Light does not need a medium to
travel through.
A medium is a material through which
a wave travels.
Light can travel through a vacuum.
An example of a vacuum is the
space between Earth and the Sun.
Light travels at different speeds
through different mediums
Electromagnetic Spectrum
The electromagnetic spectrum includes
a range of electromagnetic waves.
Wavelengths are measured in
nanometers.
Wavelength is 400nm
Wavelength is 700nm
A light source is something that emits
(gives off) heat.
Examples of light sources include:
burning candle, sun, light bulb
A light ray is a narrow beam of light that
travels in a straight line.
Laser
A reflection is the process of light striking
an object and bouncing off.
We see things because they
reflect
light into our eyes.
Homework
Depending on how materials interact with light, they
are classified as: transparent, translucent, or opaque
Transparent:
almost all light
passes through
object
Translucent:
most light
passes through
& blurry image
forms
Opaque:
no light passes
through it
When light waves interact with matter
they can be:
1. Transmitted
light waves travel through a material
(transparent object)
2. Absorbed
light waves are converted to other
forms; translucent object
3. Reflected
light waves bounce of surface of material
(opaque object)
Law of Reflection
The angle of incidence is always equal to the
angle of reflection.
Normal
Reflected ray
Incident ray
Angle of
incidence
Angle of
reflection
Mirror
HAVE YOU EVER SEEN DUST PARTICLES FLOATING IN THE
AIR WHEN A BEAM OF SUNLIGHT SHINES THROUGH A
WINDOW?
This is an example of scattering.
Scattering occurs when light waves
travelling in one direction are made to travel
in many directions.
Refraction
Light waves change direction when they
travel from one material to another.
The bending of a wave as it moves from
one material to another is called
refraction.
This is due to a change in speed.
Light
Light is slower when passing through
dense materials.
Retina
Rods
• 120 million
• Allow you to see in dim
light
• Black and white signals –
does not allow you to see
color.
Cones
• 6 million
• Response to light waves with
different wavelengths allow
you to see different colors.
• 3 types – each detecting a
different wavelength.
• In some people, not all 3
function properly = color
blindness/color deficiency.
People with color deficiency cannot
see a number in this picture!
How your eye works
LESSON 3:
MIRRORS & LENSES
Regular Reflection
Light waves reflect off a mirrorlike surface.
The smooth surface reflects light rays
traveling in the same direction at the
same angle.
Diffuse Reflection
When a surface is not smooth the
reflected angle travels in many different
directions.
Mirrors
A mirror is any reflecting surface that forms
an image by regular reflection.
Plane Mirror:
Flat surface
Same image, just
reversed left to
right
Concave Mirror:
Curved Inward
Objects can appear
upside down or
right-side up
Convex Mirror:
Curved outward
Objects are smaller
and right-side up
Cosmetic mirrors are often
concave mirrors.
Image becomes magnified.
Convex mirrors are often used for
safety purposes.
Lens
A lens is a transparent object with at least
one curved side that causes light to change
direction
Convex Lenses
• Curved outward
• Thicker in the middle
• Objects appear larger
Concave Lens
• Curved inward
• Thicker at the sides
• Object is shown smaller
Glasses for nearsightedness (can’t see far)
How do objects get their color?
Objects reflect light.
Colors depend on the wavelengths of the
light waves it reflects.
The rose looks red
because all the
other wavelengths
are absorbed but
red is reflected.
White light is a combination of all light waves.
Neon lights emit
(give off)
different colors.
The appearance of an object changes under different lights.