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      <title>Activity 18 by GERARDO SANTIAGO GONZALEZ LOPEZ</title>
      <link>https://padlet.com/173087/euo9kftda5t3</link>
      <description>Tipes of alternative energy </description>
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      <pubDate>2018-02-13 19:18:12 UTC</pubDate>
      <lastBuildDate>2018-02-13 19:27:00 UTC</lastBuildDate>
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         <link>https://padlet.com/173087/euo9kftda5t3/wish/231245575</link>
         <description><![CDATA[<div>The sun—that power plant in the sky—bathes Earth in <a href="https://www.scientificamerican.com/article/a-solar-grand-plan">ample energy</a> to fulfill all the world's power needs many times over. It doesn't give off carbon dioxide emissions. It won't run out. And it's free.</div><div><br>So how on Earth can people turn this bounty of sunbeams into useful electricity?</div><div><br>The sun's light (and all light) contains energy. Usually, when light hits an object the energy turns into heat, like the <a href="https://www.scientificamerican.com/article/how-exactly-does-light-tr">warmth you feel while sitting in the sun</a>. But when light hits certain materials the energy turns into an electrical current instead, which we can then harness for power.</div><div><br>Old-school solar technology uses large crystals made out of <a href="https://www.scientificamerican.com/article/engineering-silicon-solar-cells">silicon</a>, which produces an electrical current when struck by light. Silicon can do this because the electrons in the crystal get up and move when exposed to light instead of just jiggling in place to make heat. The silicon turns a good portion of light energy into electricity, but it is expensive because big crystals are hard to grow.</div>]]></description>
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         <pubDate>2018-02-13 19:23:20 UTC</pubDate>
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         <author>173087</author>
         <link>https://padlet.com/173087/euo9kftda5t3/wish/231246195</link>
         <description><![CDATA[<div><strong><br>What is a solar cell?</strong><br>A solar cell is a device people can make that takes the energy of sunlight and converts it into electricity.</div><div><strong><br>How does a solar cell turn sunlight into electricity?</strong><br>In a crystal, the bonds [between silicon atoms] are made of electrons that are shared between all of the atoms of the crystal. The light gets absorbed, and one of the electrons that's in one of the bonds gets excited up to a higher energy level and can move around more freely than when it was bound. That electron can then move around the crystal freely, and we can get a current.</div><div><br>Imagine that you have a ledge, like a shelf on the wall, and you take a ball and you throw it up on that ledge. That's like promoting an electron to a higher energy level, and it can't fall down. A photon [packet of light energy] comes in, and it bumps up the electron onto the ledge [representing the higher energy level] and it stays there until we can come and collect the energy [by using the electricity].</div>]]></description>
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         <pubDate>2018-02-13 19:24:22 UTC</pubDate>
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         <link>https://padlet.com/173087/euo9kftda5t3/wish/231247301</link>
         <description><![CDATA[<div><br>Wind turbines operate on a simple principle. The energy in the wind turns two or three propeller-like blades around a rotor. The rotor is connected to the main shaft, which spins a generator to create electricity. Click on the image to see an animation of wind at work. <br><br></div><div><figure class="attachment attachment--preview"><img src="https://energy.gov/sites/prod/files/howdowindturbineswork.png" width="290" height="259"><figcaption class="attachment__caption"></figcaption></figure>Click on the image to explore how wind turbines work.</div><div><br>So how do wind turbines make electricity? Simply stated, a wind turbine works the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. View the wind turbine animation to see how a wind turbine works or <a href="https://energy.gov/eere/wind/animation-how-wind-turbine-works">take a look inside</a>.<br><br></div><div><br>Wind is a form of solar energy and is a result of the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and the rotation of the earth. <a href="https://energy.gov/eere/wind/wind-resource-assessment-and-characterization">Wind flow patterns and speeds vary greatly across the United States</a> and are modified by bodies of water, vegetation, and differences in terrain. Humans use this wind flow, or motion energy, for many purposes: sailing, flying a kite, and even generating electricity.<br><br></div>]]></description>
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         <pubDate>2018-02-13 19:26:11 UTC</pubDate>
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