From their first creation in 1947, microwave ovens have revolutionized the industrialized world. By using electromagnetic radiation microwaves are used to excite the kinetic energy of molecules thereby increasing the objects temperature.
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- Microwaves function by using waves that have a frequency of 2.45 gigahertz. These 2.45 GHz waves are created through the use of a magnetron. A magnetron creates microwaves by interacting a stream of electrons with a magnetic field. The microwaves that are emitted from the magnetron are directed into the main chamber of the microwave. Since one of the properties of microwaves is that they reflect off of metal, the main chamber where food is placed has walls made out of metal.
- The microwaves that are directed into the chamber are optimally absorbed by water in the food that is placed inside. This is a result of the water molecules in the food have an electrical distribution of charge that is not symmetrical, it is polar. In the presence of the electric field, when a force is applied to water molecules they will begin to rotate. As these water molecules rotate, they collide with other molecules where there is a transfer in kinetic energy. Since the average kinetic energy of the food that is placed inside of a microwave is increased, the food becomes hotter.
- Learn more about the engineering of microwaves below:
Using the information provided above, answer the following questions.
- What is the method of heat transfer between the microwave itself and the food inside of it: conduction, convection or radiation?
- Describe how the charge is distributed on a water molecule.
- How is the frequency of light related to wavelength?