The Wave Motion of Sound & Light Sound – parallel vibrations Light – perpendicular vibrations

Learning Objectives Compare and contrast sound & light Relate waves to energy Develop models for reflected light

What is “light”?  We are only able to see a relatively small amount of what is called electromagnetic radiation.  We see a range of wavelengths called “visible light”.

Many Wavelengths

 Visible light has wave properties.  Light waves are self- propagating which means no medium is required for the wave travel.

Practice 1)Do you think light waves are able to travel in space? What is your evidence? 2)Do you think sound waves are able to travel in space? What is your evidence?

Light Speed  All electromagnetic waves travel at the same speed in a vacuum (in space). In metricsIn miles 3 x 10 8 m/s186,000 miles/sec 3 x 10 5 km/s670 x 10 6 mph

Practice If it takes time for light to travel a distance, then are we seeing the Sun as it is now or as it was in the past?

 We see the light wave, the energy, that objects emitted in the past when we view objects (like the Sun) in the sky. It takes time for light waves to travel. Our Sun8 min. Proxima Centauri4.2 LY Sirius8.6 LY Andromeda Galaxy2.5 x 10 6 LY

Colors  We interpret particular wavelengths of visible light as particular colors. ROY G BVROY G BV

Colors & Energy  Each color of visible light corresponds to a specific wavelength, frequency, & energy. RedYellowBlue Long WavelengthShort Wavelength Low EnergyHigh Energy CoolHot

Practice 1)Which flame do you think would be hotter, yellow or blue? 2)What color are hot water handles? What color should they be?

Photons  Sometimes light is a wave and sometimes light is a particle.  A particle of light is called a photon.  A photon is energy.  Atoms emit photons.

What happens when “light” interacts with matter?  Light interacts differently with different types of matter.

When Light Interacts with Matter  Absorption: the material may take in the energy  Transmission: the energy may travel through the material

What is the law of reflection? Reflection  Light may bounce from a surface back into the original medium. Air Mirror Air Parallel Reflection

Law of reflection  Incoming light rays and outgoing light rays have the same angle with respect to the normal line. Mirror IR The law of reflection applies to all reflective surfaces.

Diffuse Reflection Practice Does the law of reflection apply to diffuse reflection?

Mirror Image  A flat mirror reflects all light rays in the same direction. (parallel reflection)  Light bounces from you to the mirror, and then from the mirror back to you.

Virtual Image  The image produced by a flat mirror is not real.  It appears: 1)Upright 2)Same size 3)Same distance 4)Left-right reversed 5)Virtual

Curved Mirrors  Convex mirrors always produce a smaller image.  Concave mirrors usually produce a larger image.

Practice Concave or Convex 1)Which mirror has the larger field of view, allowing you to see a lot of the world in the small mirror? 2)What kind of mirror is the side mirror on a car?

Prisms & Rainbows  Each wavelength of light interacts differently when it enters matter.  Visible light may be divided into colors.

Practice Which color of light interacts the most with a prism or raindrop? Why?

What is sound?  Sound is changes in air pressure that affect our ear.  We sense the compressions, how condensed the compressions are, how close the compressions are, and the rarefactions (spreading out of molecules).

Compression Waves  A sound wave is a longitudinal wave traveling through matter.  Vibrations cause compressions and rarefactions  Molecules vibrate “side-to-side” (molecules collide) In metricsIn miles 343 m/s770 mph

Practice 1)If you see lightning and then hear thunder 3 seconds later, how far away is the storm? Do we need to use distance = rate x time ? 2)In a science fiction movie, when a spaceship explodes, we see and hear the explosion as it happens. Is the science wrong?

Frequency & Pitch  We each interpret different frequencies differently.  Pitch is our individual interpretation of frequency. Humans20-20,000 Hz Dog67-45,000 Hz Cat45-64,000 Hz Guinea Pig54-50,000 Hz Bat2, ,000 Hz Goldfish20-3,000 Hz

Sound Waves & Energy

 Incoming sound wave energy is transferred  Amplitude of natural molecule vibrations increase and may vibrate apart Resonance

Resonance can make a glass sing!  If you add energy to a glass of water, the glass will resonate.  Resonance produces sound.