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EQ: How can I explain the characteristics of waves?

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Waves and Particles

How do scientific models describe light?

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16-2-1 Waves and Particles

Dual nature of light: Light must be thought of as both waves and as streams of particles because neither concept alone can explain all of it’s properties.

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16-2-2 Waves and Particles, continued

Light does not require a medium and consists of transverse electromagnetic waves with electric and magnetic fields.

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16-2-3 Waves and Particles, continued

The wave model of light explains

• how light waves interfere with one another

• why light waves may reflect

• why light waves refract

• why light waves diffract

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16-2-4 Waves and Particles, continued• The particles of light are massless photons that are packets or quanta of energy with specific frequencies.

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16-2-5 Waves and Particles, continued• The particle model of light explains

–The photoelectric effect when photons cause electrons to be emitted from metals

–Reflection

–Refraction

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16-2-6 Waves and Particles, continued

The amount of energy in a photon is proportional to the frequency of the corresponding electromagnetic wave.

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Waves and Particles, continued

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Waves and Particles, continued• The speed of light depends on the medium.

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16-2-7 Waves and Particles, continued• Intensity (brightness):

depends on the number of photons per second, or power, that pass through a certain area of space.

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The Electromagnetic Spectrum

What does the electromagnetic spectrum consist of?

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16-2-8 The Electromagnetic SpectrumThe electromagnetic spectrum consists of light at all possible energies, frequencies, and wavelengths.

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16-2-9 The Electromagnetic Spectrum• The visible spectrum is only a very small part of the electromagnetic spectrum.

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16-2-10 The Electromagnetic Spectrum• Each part of the electromagnetic spectrum has unique properties.

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16-2-11 The Electromagnetic Spectrum, continued

Radio waves have wavelengths that range from tenths of a meter to thousands of meters.

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16-2-12 The Electromagnetic Spectrum, continued• Microwaves are used in cooking and communication andhave wavelengths in the range of centimeters.

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16-2-13 The Electromagnetic Spectrum, continued• Infrared light can be felt as warmth andare slightly longer than red visible light.

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16-2-14 The Electromagnetic Spectrum, continued• Sunlight contains ultraviolet

light.

The invisible light that lies just beyond violet light falls into the ultraviolet (UV) portion of the spectrum.

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16-2-15 The Electromagnetic Spectrum, continued• X rays and gamma rays are used in medicine.

–X rays have wavelengths less than 10–8 m.

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16-2-16 The Electromagnetic Spectrum, continued

–Gamma rays are the electromagnetic waves with the highest energy. •They have wavelengths shorter than 10–10 m.