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Bond Polarity

Covalent compounds may have polar or nonpolar bonds, depending on their arrangement of atoms.

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Credit: Robert Lopez
Source: CK-12 Foundation
License: CC BY-NC 3.0

You probably have one of these sitting on your kitchen counter or built into a kitchen wall. No doubt you know how to use it to reheat leftovers or make popcorn. That familiar beeping sound means that your food is done. But how does a microwave oven work? Do you know how?

News You Can Use

  • A microwave oven produces microwaves and guides them into the oven.
  • The metal walls and metal mesh inside the oven door ensure that the microwaves can’t escape from the oven. Instead, the microwaves bounce around inside the oven and pass through the food.
  • Microwaves are electromagnetic waves, like waves of visible light. However, microwaves have lower frequencies and less energy than visible light.
  • Credit: NASA
    Source: http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
    License: CC BY-NC 3.0

    Electromagnetic spectrum - longest wavelength/lowest energy (top) to shortest wavelength/ highest energy (bottom) [Figure2]

  • If they have so little energy, how can they cook food? Watch this video to find out: http://vimeo.com/46135412

Show What You Know

Learn more about microwave ovens and how they work at the link below. Then answer the following questions.

  1. It was discovered by chance that microwaves can cook food. How did it happen?
  2. What happens when positively charged particles are exposed to an electric field? What happens when negatively charged particles are exposed to an electric field?
  3. A water molecule contains polar bonds. How does this affect the water molecule in terms of electric charge?
  4. Microwaves and other electromagnetic waves have alternating electric fields. How do microwaves affect water molecules? Why does this cause water molecules and other nearby molecules to heat up?
  5. Why does food in a microwave oven get hot?
  6. If you put food in a glass dish and heat it in a microwave oven, the food but not the dish gets hot. Explain why.
  7. You should never put metal or metal foil in a microwave oven. If food wrapped in foil were to be put in a microwave oven, it would not only be dangerous, but the food also wouldn’t get hot. Why not?

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Image Attributions

  1. [1]^ Credit: Robert Lopez; Source: CK-12 Foundation; License: CC BY-NC 3.0
  2. [2]^ Credit: NASA; Source: http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html; License: CC BY-NC 3.0

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