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18.1 Electromagnetic Waves - Leilehua High School...

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10/15/14 1 Pg 532-538 Electromagnetic waves Waves make it possible for us to: Heat up our food in the Microwave oven Take X-rays 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 wouldnt be able to see anything at all 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 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. How are they produced? Electromagnetic waves are produced when an electric charge vibrates or accelerates. 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
Transcript

10/15/14

1

Pg 532-538

Electromagnetic waves  Waves make it possible for us to:  Heat up our food in the Microwave oven  Take X-rays 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

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

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.

How are they produced?   Electromagnetic waves are produced when an electric

charge vibrates or accelerates.

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

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How they travel   Electromagnetic Radiation = Transfer of energy by

electromagnetic waves traveling through matter or across space

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

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 108 m/s   c = 3.00 x 108 m/s

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

  EM radiation sometimes behaves like a wave, and sometimes like a stream of particles.

 Wave Model

  Particle Model

Theories of Electromagnetic Radiation   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

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  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

  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 brightness Ex. Distance a paint nozzle is to the piece

The End   Write your Summary!!


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