Microwave Ovens

1. Microwave Ovens Physics 001, Section 001 John Hopkins By: Vasavi Pandey

2. The Start of the Microwave Oven • 1945; the high power microwave was discovered by accident by American engineer Percy Spencer • Spencer was working on an active radar when he discovered the chocolate in his pocket had melted because of microwaves • After that, the first food to deliberately be cooked by a microwave oven was popcorn; second was an egg • Spencer, at the time, worked for Raytheon, a major American "defense contractor" • The company filed for patency in October of 1945 for Spencer's microwave process and an oven that heated food using microwave energy • Spencer confirmed all his findings by creating a high density electromagnetic field "by feeding microwave power from a magnetron into a metal box from which it had no way to escape" • When placing food into the metal box, its temperature rose quickly

3. How It Works • Microwaves use the behavior of water molecules when subjected to electromagnetic waves • In simple terms, microwaves are electromagnetic waves with wavelengths in the range of1mm - 1m • Microwaves used for cooking are electromagnetic waves processing frequencies around the 2.45 GHz range • Electromagnetic waves are waves made up of altering electric and magnetic fields • When a positively charged electron is exposed to an electric field, it experiences a force pointing in the direction of the field • When a negatively charged electron is exposed to the same field, it experiences a forced pointing in the opposite direction of the field • Since an electromagnetic wave (like a microwave) is made up of alternating electric fields, a charge exposed to it will experience forces in changing directions

4. How It Works (Cont.) • For water molecules, which are dipoles, the net effect would force the molecules into rotation • Since the fields are alternating, the rotation will change from clockwise to counter-clockwise at regular time intervals • The water molecules then possess heat energy that rub off of nearby molecules --thus heating the entire body uniformly • Electromagnetic waves in the microwave range are most suitable for this because the water molecules readily rotate when exposed to such frequencies. • This goes on and heats up the food inside the microwave

5. Various Uses for the Microwave Oven • Dry up herbs • Roast garlic • Make popcorn • Soften sugar • Steralize garden soil • Dye fabric • Decrystalize Honey • Create a giant crayon

6. The Microwave and Physics 001 • The microwave oven uses microwaves, a form of a wave • Researching the microwave oven goes further into learning about waves and understanding how they work • This relates also to what type of wave an electromagnetic wave is in relation to other waves What I Learned • It was really interesting to learn about the microwave oven because I never really understood how the device worked • A microwave is an every day device that no one really puts much thought into; we just use it and take it for granted • It was nice to understand what goes into making a microwave oven • I learned how electromagnetic waves and water molecules are both used together to get a microwave working. Before researching the device, I never would have put the two together. I also learned how the device heats up food items. I also got even a stronger understanding of waves

7. Bibliography • "Electromagnetic Waves." Drexel. Drexel, 12 May 2011. Web. 20 Apr. 2014. <http://www.physics.drexel.edu/~gyang/How/lecture_051111.pdf>. • VILLANUEVA, JOHN C. "How Do Microwaves Work." Universe Today. N.p., 18 Nov. 2009. Web. 19 Apr. 2014. <http://www.universetoday.com/45527/how-do-microwaves-work/>.