What do you remember from the previous unit about waves?

WAVES What do you remember from the previous unit about waves?

Brainstorm How many kinds of waves can you think of?

Water waves Light waves Sound waves Earthquake waves Slinky waves Microwaves X-rays waves Gamma waves A “good morning wave” is different. A stadium wave is also different, but models wave motion. Examples of Waves

What do all waves have in common? Waves transport energy.

Some waves are made up of invisible things called electric fields and magnetic fields These waves all called electromagnetic waves.

Electromagnetic Waves • All electromagnetic waves travel at the same speed but they have different wavelengths and different frequencies. • Example: radiation in wavelengths that your eyes can see is called visible light.

Electromagnetic Spectrum • Electromagnetic spectrum is the name for the range of electromagnetic waves when they are placed in order of increasing frequency. • The electromagnetic spectrum is made of radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays.

Which electromagnetic waves have longer wavelengths? Radio Waves Which electromagnetic waves have shorter wavelengths? Gamma Rays http://dawn.artov.rm.cnr.it/img/spectrum.jpg

Radio Waves • Have longest wavelength. • Antennas pick up radio waves from the air and send them through wires to your radio. • Radio converts electromagnetic waves into sound that comes out of speaker.

Infrared Rays • Shorter wavelength and higher frequencies than radio waves. • You can feel the longest infrared rays as warmth (so they are often called heat rays). • Heat lamps have bulbs that give off more infrared rays and less visible light than regular bulbs.

Visible Light • Shorter wavelengths and higher frequencies than radio waves. • Longest wavelengths are red; shortest wavelengths are purple or violet. Arrange the color spectrum from longest to shortest wavelength?

Ultraviolet Rays • Ultraviolet rays have higher frequencies than visible light so they carry more energy. • This high level of energy is enough to kill or damage living cells. • UV rays present in sunlight can burn your skin; too much exposure can cause skin cancer and damage your eyes

X-Rays • Very short wavelength • High frequency, therefore they carry more energy than ultraviolet rays and can penetrate most matter.

Gamma Rays • Shortest wavelengths and highest frequencies • The most penetrating of all of the electromagnetic waves • Can be used to kill cancer cells in radiation therapy

Uses for Waves • Microwaves • Microwave ovens give off electromagnetic waves that bounce around in the oven and penetrate the food • X-rays • Used to make images of bones inside the body • X-rays penetrate skin and tissues, but not bone because of its density (the bone absorbs the rays)

Light • Light can be thought of as traveling in rays, which move in straight lines until they hit something. • When light strikes an object, it can be reflected, absorbed or transmitted.

Dark Colors vs. Light Colors • Darker colors absorb more of the light that hits them than lighter colors. • Light is energy therefore absorbing light makes the temperature increase.

Reflection • You can see most objects because light reflects (or bounces) off of them. • Reflection is the bouncing back of a wave when it hits a surface that it can not pass through.

Refraction • When light rays enter a new medium at an angle, the change in speed causes them to bend or change direction. Refraction at the water surface gives the "broken pencil" effect shown above. Submerged objects always appear to be shallower than they are because the light from them changes angle at the surface, bending downward toward the water. http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/optpic/brokpen.jpg

Reflection or Refraction??? A B

What causes a rainbow? • Rainbows occur when raindrops & sunshine cross paths. • When sunlight (which contains all colors of light) enters water drops, it reflects off of its inside surfaces. • Light passes through drops and separates into its component colors

Refraction and Speed of Light • When light passes from air into water, light slows down. • Light slows even more when it passes from water to glass. • When light passes from glass back into air, the light speeds up.

Common Uses of Light • Telescopes • Use lenses & mirrors to collect and focus light from distant objects • Microscopes • Uses combination of lenses to produce and magnify an image

Common Uses of Light • Lasers • Consists only of light of one color • CD’s: laser shines on surface of cd and is reflected to play the music on the cd. • Surgery: use lasers to make incisions; reduces blood lost by patients and heal faster

Clap your hands together gently. What caused the sound that you heard?

Sound • Sound begins with a vibration. • Sound waves travel through the air. • Each molecule in the air moves back and forth as the disturbance (wave) goes by.

Sound • Sound can travel through solids and liquids. • When you knock on a door, the particles of the door vibrate. • The vibration creates sound waves that travel through the door. • When sound waves reach the other side of the door, they make sound waves in the air on the far side.

Frequency • Frequency of a sound wave is the number of vibrations that occur per second. • Most people can hear frequencies between 20 Hz and 20,000 Hz

Pitch • Pitch is a description of how high or low the sound seems to a person. • The pitch of a sound that you hear depends on the frequency of the sound wave. • High frequencies have high pitch while low frequencies have low pitch

Pitch • Think of a string instrument. • The tighter strings produce high frequencies; you hear these high frequencies when you hear a sound with a higher pitch. • Different lengths of strings produce different frequencies also. • Short strings produce higher pitch than longer strings

What are some similarities and differences in sound and light waves?

What do you remember from the previous unit about waves?