This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I've included it here so you can participate and learn!

Discover the world of clean, renewable energy that scientists are developing today! Explore how they are harnessing the energy of tides and waves, lean how cars can run on just sunlight and water, tour a hydroelectric power plant, visit the largest wind farms on the planet, and more! You’ll learn how streets are being designed to generate electricity, how teenagers are making jet fuel from pond scum in their garage, and how 70 million tons of salt can provide free, clean energy 24 hours a day forever! During class, you’ll learn how to bake solar cookies, magni-fry marshmallows and do the experiment with light Einstein won a Nobel prize for that is the basis of all photovoltaic energy today.

Materials:

• One cup each: hot (not boiling), cold, and room temperature water
• Cardboard box, shoebox size or larger.
• Aluminum foil
• Plastic wrap (like Saran wrap or Cling wrap)
• Hot glue, razor, scissors, tape
• Wooden skewers (BBQ-style)
• Black construction paper
• Cookie dough (your favorite kind!)
• Chocolate, large marshmallows, & graham crackers if you want to make s’mores! If not, try just the large marshmallow.
• Large page magnifier (also called a Fresnel lens, found at drug stores or places that also sell reading glasses, or at Amazon.com)

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What's Going On?

For the main experiment:

The Fresnel ("FRAY-nell") lens is a lot like a magnifying glass. Convex lenses (like a handheld magnifier) are thicker in the middle - you can actually feel it with your fingers. A Fresnel lens was first used in the 1800s to focus the beam in a lighthouse. It has lots of ridges you can feel with your fingers. It's basically a series of magnifying lenses stacked together in rings (like in a tree trunk) to magnify an image.

The Fresnel lens in this project is focusing the incoming sunlight much more powerfully than a regular hand held magnifier. But focusing the light is only part of the story with your roaster. The other part is how your food cooks as the light hits it. If your food is light-colored, it's going to cook slower than darker (or charred) food. Notice how the burnt spots on your food heat up more quickly!

The best thing about Fresnel lenses is that they are lightweight, so they can be very large (which is why light houses used these designs). Fresnel lenses curve to keep the focus at the same point, no matter close your light source is.

Questions to Ask

• What other kinds of food can you roast with your setup?
• Does a white marshmallow or chocolate-covered marshmallow cook faster? Why?
• Does it matter what angle you point your roaster at?
• Will it work with an indoor light?
• Why do you need the foil? Can you skip it?
• Do we have to use a Fresnel lens? What about a handheld magnifier - would that work?

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