Agenda:

• Notes on Light and Electromagnetic Waves
• SWBAT understand the ordering of the frequency, wavelength, and energy for the various regions in the continuous spectrum for electromagnetic waves and visible light waves.

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Homework:

• Reading/Questions

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Electromagnetic Waves

• Electromagnetic Waves: waves that do not need matter (or medium) to transfer energy.
• Examples: radiation, TV & radio waves, x-rays, microwaves, lasers, energy from visible light
• Electromagnetic(E&M) waves travel at 3 x 10⁸ m/s, 300,000km/s, or 186,000 miles/s through a vacuum.
• That’s more than 7 times around the Earth in a second

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Sooo…Why do you see lightning before you hear thunder?

NOTES: Types of E-M Waves

• The difference between electromagnetic waves is the wavelength & frequency only. The speed for each wave type is the same.
• Radio waves have the longest wavelength.
• Gamma waves have the shortest wavelength.
• Microwaves help to heat food and see into outer space by the movement of molecules.
• Infrared
• Heat

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• Visible light (white light) can be separated into the colors of the rainbow.
• Red has the longest wavelength.
• Violet has the shortest.
• Ultraviolet waves
• Cause tans and sunburns
• X-rays – pass through soft tissues. take pictures of shadows of bones.
• Gamma - Used to sterilize items

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• E-M waves are produced by
• An accelerating ion
• An accelerating proton
• An accelerating electron
• what do the three objects above have in common?�accelerating charged particles (whose movement causes waves)
• E-M waves travel faster than sound waves

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• Electromagnetic Spectrum: illustrates the range of wavelengths and frequencies of electromagnetic waves

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1. Which of the following has the longest wavelength:
1. Microwave (b) gamma ray (c) radio wave (d) ultraviolet light

2. Which of the following has the highest frequency:

(a) Microwave (b) gamma ray (c) radio wave (d) ultraviolet light

3. Compare the wavelength and frequency of a radio wave to the wavelength and frequency of a gamma ray

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4. Compare the wavelength of infrared light to the wavelength of ultraviolet light

Light Carries Energy

• Early 1600s: Robert Hooke said light travels in small, rapid vibrations (in “wavelike” motion)

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• 1700s: Sir Isaac Newton proposed that light travels as small particles

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• Today: we think of light as acting like both a wave and a particle.
• Watch a great Veritasium video on wave and particle behavior: https://www.youtube.com/watch?v=GzbKb59my3U

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Why are there different colors of light?

Different colors are due to different wavelengths of light

Substances have a tendency to reflect or refract some wavelengths more than others.

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Different wavelengths carry different amounts of energy

Predict: which color carries the most amount of energy? Why?

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TEST YOUR KNOWLEDGE!

Out of these two apples, which color has more energy?

TEST YOUR KNOWLEDGE!

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Green! Because it has a shorter wavelength (all peaks are same height, therefore, more peaks = more energy)

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TEST YOUR KNOWLEDGE!

Which color reflects more energy?

“BY CANDLELIGHT”

Observe:

• How would it feel to put your hand near the candle?
• Draw the candle, indicating the colors you observe in the flame
• Label the hottest and coldest parts/colors. Compare those parts to the wavelengths for each color. Is there a similarity in the pattern?

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• Explanation:
• Light is made up of colors of different wavelengths. Each wavelength contains a different amount of energy.
• Longer wavelengths (red, orange, yellow):

more/less energy?

• Shorter wavelengths (blue, violet):

more/less energy?

• What color would be the hottest flame? Why?

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1. Just like a wave, light carrie
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s energy!

• Just like a particle, light has no mass!

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THE END