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Let There Be Light…Explained!

Electron ConfigurationIntroduction

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What is Light? (Basic Version)

Light is a wave that transports energy from one place to anther. It is a type of “Electromagnetic Radiation” (EM)

What does this mean?1. It has to do with electrons.2. It is related to magnetism.3. It is a form of energy.

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How is light produced

It’s actually pretty simple (and really amazing):1. The electrons orbit the nucleus in specific energy

levels (aka “The Ground State”).2. When the atom absorbs a specific amount of energy,

the electrons move to higher energy levels (aka “The Excited State”)

3. They can’t stay there for long, so they fall back down to The Ground State, and release the energy they absorbed...

AS LIGHT!

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How The Process Happens

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There are many kinds of light.

Visible light, that you can see with your eyes is just a tiny smidge of a much broader phenomenon (EM radiation).We put all EM radiation on a “spectrum” from the lowest energy to the highest:

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What is Light? (Extended Remix)1. EM Radiation is made of photons.2. Photons travel really fast (3.00 x 108 m/s), and only

have mass when they are moving.3. Nothing can travel faster than photons.4. Made up of electric and magnetic waves traveling

perpendicular to each other.5. We focus on three properties of EM waves:

I. The Wavelength (λ)II. The frequency (f)III. The Energy (E)

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Wavelength (λ)Wavelength is defined as the distance from one point on a wave to the same point on the next wave.Amplitude is defined as the distance from equilibrium to the top of the wave. (measured in meters)We measure light wavelengths in meter derivatives (just like we measure any length with).Radio Waves:

~103 mVisible Light:

~10-7 mGamma Rays:

~10-12 m

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Frequency (f)

Frequency is defined as the number of wavelengths that pass a point in space per second. We measure frequency in Hertz (cycles per second).Radio Waves: ~ 104 HzVisible Light: ~ 104 HzGamma Rays: ~ 1020 Hz

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Here’s What You Need To Know:The more energy a light wave has the higher its frequency (a direct relationship). The more energy a light wave has the smaller its wavelength (an indirect relationship).

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A Little Light Mathematics.The relationship between frequency and energy of an EM wave is directly proportional.The equation that describes this relationship is:

This is NOT on Your Reference Tables !!!

E = hfE = Energy (Joules)h = Planck’s Constant (6.63 x 10-34J s)f = frequency (Hz)

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What is the energy of a photon of red light with a frequency of 4.70 x 1014 Hz?

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An electron drops in energy levels by 2.31 x 10-15 J. What is the frequency of the photon it gives off?

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A Little More Light Mathematics.The relationship between frequency and wavelength of any wave is inversely proportional.For light waves, the formula that describes this is:

This is NOT on Your Reference Tables!!!

f λ = cf = frequency (Hz)λ = wavelength (m)c = speed of light (3.00 x 108 m/s)

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The most popular VHF band used by ham radio operators is the 2.00 m band. What is the frequency of a photon with this wavelength?

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The frequency of the radio waves emitted by the WYRK Radio Tower is 106.5 MegaHertz. What is the wavelength of those radio waves?

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Back to Bright Line Spectra

As Niels Bohr noticed, when you give a sample of an element some energy, it emits characteristic spectra. It doesn’t produce all of the wavelengths of light.

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Why?

Remember that electrons can only go to specific energy levels when they absorb energy. As a result, they can only emit specific wavelengths of light when they fall back to the ground state.That’s why.We can use this fact to identify the elements thatare in distant galaxies, by looking at the light fromthose galaxies.

Emission Spectra

• Each element has its own line spectrum just as each person has its own fingerprint.

• Each line on the spectra represents the enrgy lost as an electron goes from a higher energy level to a lower energy level.

• This energy is related to the frequency and hence related to a specific “color” of the electromagnetic spectrum.

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What now?

Any Questions?