Switch on the microwave oven, and you are switching on a powerful magnetic field which oscillates in the same frequency band that is used for radio broadcasts and radar. Microwaves in the field can be used to cook food rapidly by making the water molecules in the food vibrate at almost 2500 million times a second. This action absorbs energy from the magnetic field and heats the food.
As all the energy is absorbed by the food and not wasted on heating the surrounding air on the oven itself, the process is far quicker and more economical than traditional cooking methods.
The microwave energy does not heat the utensils in the oven because the materials they are made of such as China and glass do not absorb energy from the magnetic field. However, the plates do not come out of the oven cold, because they are heated by the food.
Special cookware
Many other materials besides China and glass can be used in a microwave oven – such as plastic, paper and cardboard. And special cookware – which is transparent to microwaves – has been developed for use in microwave ovens.
Metal container should not be used because metal does not transmit microwaves but reflects them. So foods should not be covered with aluminium file. Wooden utensils are also best avoided in microwave ovens because wood always contains some moisture, and this can cause it to split when it heats up.
Long wave radio waves have a wavelength measured in thousands of metres. The microwaves used in microwave ovens have a wavelength of about 5in (120 mm).
An electromagnetic wave is a vibration of electrical and magnetic fields, constantly going from negative to positive. Microwave oven is operate with the waves that vibrate 2450 million times a second- a frequency of 2450 megahertz MHZ.
Water molecules have a positively charged end and negatively charged end. The vibrating positive negative microwaves interact with the positive negative water molecules, attracting and repelling them and making them twist first one way, then the other. This also happens 2450 million times a second.
The most important part of the microwave oven is the electronic tube, or magnetron, that generates the microwaves. The magnetron was developed in 1940 by British researchers at Birmingham University, and was first applied usefully in radar. It’s domestic potential was first realised buy the Raytheon Company in the United States in the early 1950s.
Picture Credit : Google