1. Chp 18.1 - Electromagnetic Waves Pg 532-538

2. Electromagnetic waves  Waves make it possible for us to:  Heat up our food in the Microwave oven  Take xrays of our bones and teeth  Watch television and get our favorite music to our radio  Carry cell phone conversations  See different colors  Without light waves we wouldn’t be able to see anything at all  Waves make it possible for us to:  Heat up our food in the Microwave oven  Take xrays of our bones and teeth  Watch television and get our favorite music to our radio  Carry cell phone conversations  See different colors  Without light waves we wouldn’t be able to see anything at all

3. Electromagnetic Waves  Are transverse waves consisting of changing electric fields and changing magnetic fields  Carry energy from place to place like mechanical waves but differ in how they are produced and how they travel  Are transverse waves consisting of changing electric fields and changing magnetic fields  Carry energy from place to place like mechanical waves but differ in how they are produced and how they travel

4. How are they produced?  Produced by constantly changing fields  An electric field in a region of space exerts electric forces on charged particles.  Electric fields are produced by  electrically charged particles  changing magnetic fields.  A Magnetic field in a region of space produces magnetic forces  Magnetic fields are produced by  Magnets  changing electric fields  vibrating charges.  Produced by constantly changing fields  An electric field in a region of space exerts electric forces on charged particles.  Electric fields are produced by  electrically charged particles  changing magnetic fields.  A Magnetic field in a region of space produces magnetic forces  Magnetic fields are produced by  Magnets  changing electric fields  vibrating charges.

5. How are they produced?  Electromagnetic waves are produced when an electric charge vibrates or accelerates.

6. How they travel  Because changing electric fields produce changing magnetic fields, and changing magnetic fields produce changing electric fields, the fields regenerate each other  As they regenerate, their energy travels in the form of a wave  Electromagnetic waves do not need a medium to travel through  Electromagnetic waves can travel through a vacuum, or empty space, as well as through matter  Because changing electric fields produce changing magnetic fields, and changing magnetic fields produce changing electric fields, the fields regenerate each other  As they regenerate, their energy travels in the form of a wave  Electromagnetic waves do not need a medium to travel through  Electromagnetic waves can travel through a vacuum, or empty space, as well as through matter

7. How they travel  Electromagnetic Radiation = Transfer of energy by electromagnetic waves traveling through matter or across space

8. Michelson’s Experiment  In 1926 Albert Michelson measured the speed of light more accurately than ever before  Completed his experiment on the top of Mount Wilson in California  Shined a bright light and used a stationary mirror and a rotating mirror 53.4 km away. With his values he calculated the speed of light quite accurately  In 1926 Albert Michelson measured the speed of light more accurately than ever before  Completed his experiment on the top of Mount Wilson in California  Shined a bright light and used a stationary mirror and a rotating mirror 53.4 km away. With his values he calculated the speed of light quite accurately

9. Speed of Electromagnetic Waves  When a thunderstorm is approaching you can see the sky light up before you hear the thunder rumble  As the storm comes closer the time between when the flash occurs and the rumble begins becomes smaller  Light travels much faster than sound  Light and all Electromagnetic waves travel at the same speed in a vacuum  The speed of light in a vacuum or c is equal to 300,000,000 m/s. Or 3.00 x 10 8 m/s  c = 3.00 x 10 8 m/s  When a thunderstorm is approaching you can see the sky light up before you hear the thunder rumble  As the storm comes closer the time between when the flash occurs and the rumble begins becomes smaller  Light travels much faster than sound  Light and all Electromagnetic waves travel at the same speed in a vacuum  The speed of light in a vacuum or c is equal to 300,000,000 m/s. Or 3.00 x 10 8 m/s  c = 3.00 x 10 8 m/s

10. Wavelength and Frequency of Electromagnetic Waves in a vacuum  Electromagnetic Waves vary in wavelength and frequency  The speed of an electromagnetic wave is the product of its wavelength and frequency  Speed = wavelength x frequency  As the wavelength increases, the frequency decreases  Electromagnetic Waves vary in wavelength and frequency  The speed of an electromagnetic wave is the product of its wavelength and frequency  Speed = wavelength x frequency  As the wavelength increases, the frequency decreases

11.  EM radiation sometimes behaves like a wave, and sometimes like a stream of particles.  Wave Model  Particle Model Theories of Electromagnetic Radiation

12.  In 1801, Thomas Young showed that light behaves like a wave  Interference only occurs when two or more waves overlap  Double Slit Experiment - pass light through two slits and an interference pattern is observed  Constructive Interference – an overlap in waves cause an increase in amplitude  Destructive interference – an overlap in waves cause a decrease in amplitude Evidence for Wave Model

13.  Photoelectric Effect - light striking a metal can cause electrons to be emitted from the metal  Photons – are packets of electromagnetic energy  The greater the frequency of an EM wave, the more energy each of its photons have  Blue light has a higher frequency than red light so photons of blue light have more energy than photons of red light  Blue light causes emissions of electrons from metal but red light does not because blue light is higher energy Evidence for the Particle Model

14.  The closer you are to a source of light the brighter the light appears  Intensity is the rate at which a wave’s energy flows through a given unit of area – (brightness of light)  Intensity of light decreases as photons travel farther from the source What is Intensity of light? Ex. Flashlight’s brightnessEx. Distance a paint nozzle is to the piece

15. The End  Write your Summary!!