Sound and Light
Spectra of Science
Amole
2013
Sound Waves
• Produced from vibrating particles
– Particles “bump” into each other to transfer the energy
through the medium
• Travel in longitudinal waves
• Travel in all directions (like a circle)
• Can travel through solids, liquids, and gases
– Faster in solids and liquids than gases
• Cannot travel in a vacuum
(through empty space)
Sound Examples
• Percussion instruments have vibrating
membranes
• String instruments have vibrating strings
• Woodwinds have vibrating reeds
• Brass instruments vibrating lips
• Your vocal cords are two thin elastic bands that
vibrate
– Say “ahhhhh” and touch your throat. Feel them?
Pitch
• How high or low a sound is
• Determined by frequency of the sound wave
• Frequency is determined by how quick or slow
the particles vibrate
Quick Vibration
High Frequency
High Pitch
Slow Vibration
Low Frequency
Low Pitch
Notice: High frequencies have shorter wavelengths.
Intensity
• Determines the “loudness” of the sound
• Intensity decreases with distance from the sources
as it spreads out
• Depends on the amplitude of the sound
• Higher amplitudes produce louder sounds
Louder
Softer
Notice: The wavelength and frequency are the
same. Only amplitude changed.
Hearing Sound: The Ear
1. Sound causes your
eardrum to vibrate.
The eardrum
vibrates differently
for each sound.
2. The bones of your
ear begin to vibrate,
beginning with the
hammer, moves to
the anvil, and finally
the stirrup
Eardrum
3 bones:
hammer,
anvil, and
stirrup
Hearing Sound: The Ear
Cochlea
Outer Ear
3. The sound energy
passes to the inner
ear. This causes the
fluid in the cochlea
to move.
4. The nerves then
carry the message
to the brain. Your
brain then tells you
what the sound is.
Inner Ear
Producing Sound: The Vocal Chords
1. Air from the lungs
flows through the
windpipe and into the
voice box (where the
vocal cords are).
2. Then the air pushes
the vocal cords apart
making them vibrate.
3. The vibrations create
a series of sound
waves that exit
through your mouth.
Producing Sound: The Vocal Chords
4. The change of shape of the vocal cords
changes the sound and its pitch.
5. If you can’t talk because of a cold or
laryngitis, it is because your vocal cords are
swollen and inflamed.
More About Sound
• Sonar- Sound Navigation And Ranging
– Determine distance by measuring the time it takes for
sound waves to be reflected back
– Used by ships, submarines, and bats
• Ultrasound
– Use echos to produce images called sonograms of inside
the body without performing surgery
Did You Know?
• Sound waves that are reflected off boundaries
are called “echos.”
• Sound travels 4 times faster in water than air.
• Any frequency of sound below the range of
human hearing (20 Hz) is called Infrared
sound.
• Any frequency of sound above the range of
human hearing (20, 000 Hz) is called
Ultrasound.
Doppler Effect
• Change in frequency of a wave due to relative
motion between source and observer.
• A sound wave frequency change is noticed as a
change in pitch.
• http://ls.xenia.k12.oh.us/SafeVideos/Video.aspx?i
d=Tn35SB1_NYI
Light Waves
•
•
•
•
“Dual natured”
Travel in transverse waves
Travel in straight lines in all directions
Can travel through some solids, liquids, and gases
– Slow down when traveling through a medium
• Can travel in a vacuum (through empty space)
– Consist of changing electric and magnetic fields in space
Where does light come from?
Our major
light source:
the Sun
Electromagnetic Spectrum
Two Models of Light
• Wave Model
– Transverse waves that do not need a medium
– Explains why light can reflect, refract, or diffract,
interfer with one another, and produce standing
waves
• Stream of Particles Model
– Photons- packets of light, localized energy
– Explains why blue light can knock electrons off a metal
plate but red light cannot, and why light can travel
without a medium
• The model used depends on the situation
Energy and Frequency
• Energy of light is proportional to frequency
• Higher frequency = more energy
The Speed of Light
• In a vacuum, all light travels at the same speed
– 3 x 108 m/s = 186,000 miles/sec
– Symbol “c”
– Light is the fastest signal in the universe
• Also can travel through transparent mediums
– Air, water, and gas
– Travels slower when passing through a medium
– More dense = slower speed
Intensity
• Determines the “brightness” of light
• Intensity decreases with distance from the
sources as it spreads out
• Depends on amount of light (number of
photons or power passing through)
Intensity
How Light Travels
 Light rays travel in straight lines from the light source.
 When it hits an opaque object, some light is absorbed and
the rest reflects off.
 If the object is transparent, light rays pass through it
easily.
 If the object is translucent, some light can pass through,
but the rest of the light will be reflected.
Reflection
Angle of incidence
Angle of reflection
The ‘angle of
reflection’ is
always equal
to the ‘angel
of incidence’.
Seeing Color
• The colour an object appears depends on the colours of
light it reflects.
For example, a red book only reflects red light:
White
light
Only red light is
reflected
Colors
• White light can be split up to make separate colours.
These colours can be added together again.
• The primary colours of light are red, blue and green:
Adding blue and red
makes magenta
(purple)
Adding red and
green makes
yellow
Adding blue and green
makes cyan (light blue)
Adding all three
makes white
again
A pair of purple trousers would reflect purple light (and red and
blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colours:
White
light
Refraction
•Waves travel different speeds in
different mediums
•When waves change mediums, their
speed changes causing the waves to
bend
Diffraction
light
source
 Light
light
source
rays travel in straight lines, radiating out from the
light source.
 If rays are blocked by an opaque object a shadow forms
where the light cannot reach.
 If the light source is moved closer to the object, more
light is blocked and a larger shadow is formed.
Shadows
2pm
The position of the
Sun effects
3pm the
position and length of
the shadows created.
4pm
7pm
...and travel
across the sky
until it sets in the
West.
12am
10am
Looking North,
the Sun appears
to rise in the
9am
East...
8am
6am
Thanks to this
natural phenomenon a
sundial is able to tell
us the time, as long
as it is a sunny day!
Seeing Light: The Eye
1. Light coming from, (or
reflecting off) objects enters
the eye through the cornea
then the pupil.
2. It is focused clearly by the
lens on to the retina.
3. The light sensitive cells of
the retina gather
information about patterns
of light and dark, color and
movement and send it
through the optic nerve.
Seeing Light: The Eye
3. Information entering the brain
through the optic nerve, is
then transmitted through
more nerve pathways to the
visual cortex.
4. Here the patterns of light and
dark, colour and movement
are interpreted.
5. The brain, based on past
experience, can then
understand what it ‘sees’.
More about Light
• Sunlight contains ultraviolet and infrared
– UV will burn you, IR warms you
• X-rays and gamma rays are high frequency
light waves used in medicine
• Microwaves are used in cooking and
communication (mobile phones)
• Radio waves are used in communication
and radar
– Radar: Radio Detection And Ranging
– Uses reflected radio waves to determine
velocity and location
Did You Know?
• Rainbows are the refraction of white
light through water droplets that
reflect them back in the air.
• Fiber optics operate on total internal
reflection.
• The interference of light waves
create the rainbow swirls on bubbles.
• The light we see from the sun is 8
minutes old. It takes light 8 minutes
to travel from the sun to Earth even
at its fast speed.