May 22, 2014
Physics of Microwaves
Microwaves are used in our everyday lives but most most people don't realize that physics plays a large and important part in the simple household item. Whenever we heat our food we are oblivious to the forces that cause such a thing to occur and we don't fully understand what happens in front of our eyes and how our food really gets heated in such a simple and efficient way.
The first thing people need to understand is that microwaves are actually electromagnetic waves. Wavelengths and frequencies range from 300 MHz up to 300 GHz but, the average microwaves at home or restaurants operate at frequencies of about 2.45 GHz. ...view middle of the document...
The efficiency percentage for this is also about 80% and lifetimes of around 5000 hours on average.
In order for food to actually begin to start heating up, the microwaves must pass pass through the food and so we must delve deeper into the magnetron. Microwaves have to have a source and that source is the device known as the magnetron. The magnetron is basically an electric field existing in the gap os the device. Magnetrons also consist of a cylindrical cathode running through the centre and the outside of the tube, formed by several cavities acting as anode and takes shape. With all this it allows the electric field to exist at the center. Perpendicular to the electric field is where the parallel to the tube length is where the permanent electric field. Located in the cathode, electrons are stripped into the electric field due to the thermionic emission which is high temperatures in the cathode exciting the electrons to make it be released. Once this is done they are accelerated to the anode, the outside of the tube, because of the forces applied to them from the electric field. Another force is also applied to them as they are on their way which is the magnetic field and this curves their motion. With their curved motion the places where there are excess negative charges in the anode is where the electrons are pushed towards. Negatives charges are then pushed back and around the cavity creating an oscillation of electric and magnetic fields caused by the moving electrons and charges. The waves emitted from the magnetron are faced towards the spinning propellor that is made of metal. Metal is crucial because one of the properties of microwaves is that it can be reflected off of metal objects and then eventually makes it to the oven chamber which begins heating your food.
The chemicals in food are also important because the microwaves are absorbed by them. Water is a very big one because it is polar which is basically saying that the distribution of charge within the molecule is not symmetrical and both sides are slightly positive and negative. With the presence of the microwaves a force can be applied to both sides of the molecule allowing it to rotate which allows them to bump into other molecules letting each one transfer kinetic energy to one another making your food hot. Thanks to the Kinetic Particle Theory you can figure out that if the food has more kinetic energy the hotter it will...