Warm Up

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# Warm Up - PowerPoint PPT Presentation

Warm Up. 1. What is energy? 2. What is kinetic energy? How do you calculate it? 3. What is potential energy? 4. What is a transverse wave? Draw and label. 5. What is a longitudinal wave? Draw and label. . Electromagnetic Waves.      . Waves… a review.

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Warm Up
• 1. What is energy?
• 2. What is kinetic energy? How do you calculate it?
• 3. What is potential energy?
• 4. What is a transverse wave? Draw and label.
• 5. What is a longitudinal wave? Draw and label.

### Electromagnetic Waves



Waves… a review
• Most waves are either longitudinal or transverse.
• Sound waves are longitudinal.
• But all electromagnetic waves are transverse…

?

?

Nature of Electromagnetic Waves
• They are Transverse waves without a medium. (They can travel through empty space)
• They travel as vibrations in electrical and magnetic fields.
• Speed of electromagnetic waves = speed of light: 300,000,000 meters/second

(Takes light 8 minutes to move from the sun to earth {150 million miles} at this speed.)

When an electric field changes, so does the magnetic field. When one field vibrates—so does the other.
• RESULT-
• An electromagnetic

wave.

• Click here Animation: Interaction of vibrating charges
Waves or Particles
• Electromagnetic radiation has properties of waves but also can be thought of as a stream of particles.
• Example: Light
• Light as a wave: Light behaves as a transverse wave which we can filter using polarized lenses.
• A “particle” of light is called a photon
Waves of the Electromagnetic Spectrum
• Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency

ULTRAVIOLET RAYS

INFRARED RAYS

GAMMA RAYS

X-RAYS

VISIBLE LIGHT

MICROWAVES

• A. Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.
• B. A radio picks up radio waves through an antenna and converts it to sound waves.
• C. Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency.
• D. MRI (MAGNETIC RESONACE IMAGING)
• Uses Short wave radio waves with a magnet to create an image

AM=Amplitude modulation—waves bounce off ionosphere can pick up stations from different cities.

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FM=Frequency modulation—waves travel in a straight line & through the ionosphere--lose reception when you travel out of range.

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MICROWAVES
• Microwaves—have the shortest wavelengths and the highest frequency of the radio waves.
• Used in microwave ovens.
• (Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food.)
• Used by cell phones and pagers.
• (Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.)
INFRARED RAYS
• Infrared= below red
• Shorter wavelength and higher frequency than microwaves.
• You can feel the longest ones as warmth on your skin
• Heat lamps give off infrared waves.
• Warm objects give off more heat energy than cool objects.
• Thermogram—a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off. Therefore people give off infrared rays.

Night vision goggles

• Remote controls
Warm Up
• 1. Draw the EM spectrum.
• 2. What is a medium?
• 3. Do EM waves need a medium to travel?
• 4. What is a “vacuum”?
• 5. What is a niche? Give an example.
• 6. What is ecology?
VISIBLE LIGHT
• Shorter wavelength and higher frequency than infrared rays.
• Electromagnetic waves we can see.
• Longest wavelength= red light
• Shortest wavelength= violet (purple) light
• When light enters a new medium it bends (refracts: we’ll talk about this tomorrow). Each wavelength bends a different amount allowing white light to separate into its various colors ROYGBIV.
ULTRAVIOLET RAYS
• Shorter wavelength and higher frequency than visible light
• Carry more energy than visible light
• Used to kill bacteria. (Sterilization of equipment)
• Causes your skin to produce vitamin D (good for teeth and bones)
X- RAYS
• *Shorter wavelength and higher frequency

than UV-rays

• *Carry a great amount of energy
• *Can penetrate most matter.
• Bones and teethabsorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed)
• Too much exposure can cause cancer
• (lead vest at dentist protects organs from unnecessary exposure)
• Used by engineers to check for tiny cracks in structures.
• The rays pass through the cracks and the cracks appear dark on film.
GAMMA RAYS
• Shorter wavelength and higher frequency than X-rays
• Carry the greatest amount of energy and penetrate the most.
• Used in radiation treatment to kill cancer cells.
• Can be very harmful if not used correctly.
Gamma Rays
• They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova explosions, and regions around black holes.
• On Earth, gamma waves are generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay.
Using the EM waves to view the Sun

Animation—View a Galaxy at different wavelengths

Song: