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lesson 13

# lesson 13 - 1 Electromagnetic Radiation(sketch out the...

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1. Electromagnetic Radiation (sketch out the spectrum in your notes) a. The form in which energy travels in space b. This energy, in the form of photons, travels in waves. When electromagnetic radiation reaches an object, it may transfer energy to that object. c. The different types of electromagnetic radiation are characterized by the frequency (or length) of the waveform . There are long radio waves of low frequency and very, very short gamma rays of high frequency. We are all familiar with the visible portion of the spectrum (visible light) but there are many more wave forms which are invisible (radio waves, microwaves, X-rays, etc). DIAGRAM: 2. 3 Principles of EMR a. 1) The shorter the wavelength, the higher the energy b. 2) The higher the energy, the greater the penetrating power, c. 3) The more complex the organism, the lower the LD50 of radiation. d. This means that forms of electromagnetic radiation with very short wavelengths will have very high energy and the ability to penetrate into matter; conversely, long wavelengths will have low energy and will not be able to penetrate matter. The third principle means that more complex organisms, such as humans, will have a lower LD50 than will simpler organisms such as bacteria. 3. Characteristics of EMR Wave Form Length (meters) Characteristics Radio waves 1 to 10,000 meters Long wave length, low frequency, low energy Microwaves 1.01 meters Visible light 10 -7 meters x-rays and gamma rays 10 -10 m to 10 -12 meters Short wavelength, high frequency, high energy 1

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4. How do microwaves work? a. An electron tube in each microwave oven (a magnetron) produces alternating pulses of microwave radiation. b. The microwaves are reflected within the metal interior of the oven and land on food where they are absorbed. The portion of food that is most affected by microwave radiation is water. c. Microwave ovens produce electromagnetic radiation of exactly the right wavelength to excite water molecules. When water molecules become excited, they heat up. d. Since most of our food contains a fair amount of water, we can heat up our food by selectively heating up the water inside the food e. Water is a dipole molecule. Water is composed of 2 hydrogen atoms and 1 oxygen atom. The hydrogen atoms are clustered together on one side of the oxygen, creating a slight imbalance in charge so that part of the water molecule is negatively charged, while the other side has a partial positive charge. f. As the microwave radiation ‘hits’ the water molecules in food, the water vibrates very rapidly, creating friction, which eventually turns the water molecule to steam and the food heats up. g. Other molecules like starch and protein, which do not have partial charges are not directly affected by microwave radiation. h. The high water content means that foods like fresh vegetables cook very quickly in a microwave oven.
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lesson 13 - 1 Electromagnetic Radiation(sketch out the...

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