Light and Sound
Sound
• Sound is a longitudinal wave
• Sound causes compressions and rarefactions
in the air molecules
• Sound must travel through a material
• Sound can not travel through empty space
• Decibels – how loud the sound is
• Decibels are determined by amplitude
(energy)
Pitch of sound
• The pitch of the sound wave depends on the
frequency of the wave
• High frequency is high pitch
• Low frequency is low pitch
Doppler Effect
• Sound
• Change in
frequency and
pitch of a sound
that is caused by
either the
movement of the
object or the
listener
• Ambulance
• Race car
Speed of Sound
• Sound travels at 340 m/s in air
• Changes speed depending on how close together the
atoms in the material are
• The speed of sound is different in different materials
– Travels fastest in solids (steel – 4512 m/s)
– Travels in between in liquids (water – 1483 m/s)
– Travels slowest in gases
• Speed also depends on the temperature
– Travels faster in warm air (100⁰F – 354 m/s)
– Travels slower in cold air (0⁰F – 320 m/s)
Supersonic
• Caused by motion that
is faster than the speed
of sound
• Silence as the object is
approaching
• Loud boom after the
object passes
• Sound is racing to catch
up
Light
• Light is created when
electrons move energy
levels inside of the
atoms
• When energy is added
to an atom the
electrons jump to
higher energy levels
• When electrons fall
back to lower energy
levels, energy is
released in the form of
light
Light
•
•
•
•
Does not need a medium to travel through
Can travel through empty space
Speed is fastest in gas, slowest in a solid
As the wavelength increases, the frequency
decreases
Theories of Light
• Particle theory – light travels as streams of
particles or photons in a straight line –
reflection
• Wave theory – light travels as waves – light
travels through openings and spreads out
• Quantum theory – a bundle of light energy
(quantum) that travels in waves
Particles, Waves or Quantum
Speed of Light
• Speed of light is
300,000,000 m/s
• Light can circle the
earth 27 times in 1
second
• Why do we see
lightening before we
hear thunder?
Photoluminescence
• Glow in the dark
• Atoms in certain
materials can store
energy when they
exposed to light
• When the light is turned
off they are no longer
storing energy and
energy is given off as
light
Electric Light
• Electricity is used to cause
the electrons to jump and
fall between levels
• Incandescent bulbs heat
metal to give off lightthey also give of heat –
less efficient
• Fluorescent bulbs heat
gases to give off light –
give off less heat – more
efficient
Colors of Light
• White light is composed of all the colors of the
spectrum – ROY G BIV
– Light from the sun is white – what happens when
it travels through a raindrop?
• Black light is the absence of all color
– Shut yourself in the bathroom with no light – can
you see any color?
Colors of Light
• Photoreceptors in the eye detect visible light
• The light we see is reflected light
• Why do we see color?
– Light that hits the shirt from the sun or a light bulb
is white
– The color of an object depends on the light wave
that is sent to our eye
– A blue shirt looks blue because blue light waves
are sent to our eye
Color in Art
• Do pigments mix the same way that light
mixes
• If I mix all the colors of pigment do I paint with
white paint
• How do I make white paint or have white
paper?
Optics
• Lenses – use refraction to bend light
• Mirrors – reflect light
• Prisms – uses refraction to separate light into
the colors
• Telescope – collection of lenses used to
magnify an object
• Laser – one specific wavelength of light that is
concentrated and organized