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Electromagnetic Spectrum

Electromagnetic Spectrum. Maxwell argued that light must be an electromagnetic waveHertz was able to produce EM waves using a spark gap with oscillating electrons at a frequency of about 109 vibrations/secondThese waves were shown to have a velocity of 3 x 108 m/sThey could be reflected, refracted and showed interference, just like light.

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Electromagnetic Spectrum

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    1. Electromagnetic Spectrum The speed of electromagnetic waves is 3 x 108 m/s As we will see later, light was shown to have wave-like properties We have studied waves in water last semester In water waves, the water itself moves at right angles to the direction of the wave The question before us is with light, what moves?

    2. Electromagnetic Spectrum Maxwell argued that light must be an electromagnetic wave Hertz was able to produce EM waves using a spark gap with oscillating electrons at a frequency of about 109 vibrations/second These waves were shown to have a velocity of 3 x 108 m/s They could be reflected, refracted and showed interference, just like light

    3. Electromagnetic Spectrum Long before people knew what light was, by doing interference measurements, people showed that visible light had wavelengths ranging from 4 x 10-7 m to 7.5 x 10-7 m Recall that f?=c where c is the velocity of light That means the frequencies of visible light range from 4 x 1014 Hz and 7.5 x 1014 Hz

    4. Electromagnetic Spectrum So, we know about two ranges of frequencies or wavelengths of EM radiation What about others? We now know that there is a very large range of frequencies and wavelengths of EM radiation in nature We can display them in a chart

    5. Electromagnetic Spectrum

    6. Measure the Speed of Light

    7. Energy in EM Waves W have determined that the energy density in an electric field is ?0E2/2 We also learned that the energy density in a magnetic field is B2/2?0 So, the energy per unit volume in space containing an EM wave is

    8. Energy in EM Waves We can do some manipulations using some of the relationships we have derived earlier to get some other forms for the energy density The energy is shared equally between the electric and magnetic fields

    9. Poynting Vector We can look at the energy transported across unit area per unit time by an EM wave

    10. Poynting Vector

    11. Poynting Vector

    12. Poynting Vector

    13. Information Transmission We can use EM waves to carry information by a technique known as modulation We are going to add two signals together Recall when we added waves together last fall, the resulting wave is just formed by addition of amplitudes This is known as amplitude modulation

    14. Information Transmission

    15. Information Transmission

    16. Information Transmission

    17. Information Transmission

    18. Information Transmission

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