MICROWAVE OVENS
Physics 001, Section 001
John Hopkins
By: Vasavi Pandey
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
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 of 1mm - 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
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
VARIOUS USES FOR THE MICROWAVE OVEN
1. Dry up herbs
2. Roast garlic
3. Make popcorn
4. Soften sugar
5. Steralize garden soil
6. Dye fabric
7. Decrystalize Honey
8. Create a giant crayon
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
BIBLIOGRAPHY
1. "Electromagnetic Waves." Drexel. Drexel, 12 May 2011. Web. 20 Apr. 2014.
<http://www.physics.drexel.edu/~gyang/How/lecture_051111.pdf>.
2. VILLANUEVA, JOHN C. "How Do Microwaves Work." Universe Today. N.p., 18
Nov. 2009. Web. 19 Apr. 2014. <http://www.universetoday.com/45527/how-domicrowaves-work/>.