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)

More Sound

• Remember Doppler Effect• Low frequency = low pitch• High frequency = high pitch• Reflection, Refraction, Diffraction and

Interference can all occur• Sound can also be absorbed

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

Sonogram

• Sonogram or Ultrasound – sound waves used to “take pictures of something we can not see”

• Ocean floor, internal organs, fetus

• Sound waves are sent out and bounce back as they hit objects

What makes Light?

• Light is made of atoms• Electrons are in energy

levels(different rings)• Electrons can move

from ring to ring• Electron moves out it

gains energy• Electrons move in they

give off energy• Energy given off = light

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

• Incandescence – making light with heat – light bulbs in our homes- not efficient

• Fluorescent – less heat more efficient

Polarization

• Light is unpolarized• Unpolarized means that

light travels in all directions• Polarizing blocks out some

of the light rays• Can block horizontal or

vertical waves• Reduced the amount of light

that reaches an object• Example - sunglasses

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