The Electromagnetic Spectrum Essay Example

  • Category:
    Physics
  • Document type:
    Assignment
  • Level:
    Undergraduate
  • Page:
    3
  • Words:
    2107

Introduction

Microwaves are electromagnetic waves that are part of creating the electromagnetic spectrum. The electromagnetic spectrum is made up of; visible light, microwaves, radio waves, ultra-violet rays, X-rays and gamma rays. These electromagnetic waves, including microwaves are all arranged in order depending on their wavelength and frequency so as to make up the electromagnetic spectrum. According to Gupta and Eugene (2007) the electromagnetic spectrum has both electric and magnetic fields hence it is able to produce the different electromagnetic waves which are formed at a right angle. Nonetheless, the speed at which these waves travel is assumed to be that of light, since each wave is defined on its wavelengths. Therefore the wave with the longest wavelength has the shortest frequency. A microwave is characterised by frequencies that range between 300 megahertz to 300 Gigahertz, whereas their wavelengths range from 1 millimetre to 1 metre (Gupta & Eugene, 2007). Sobol and Tomiyasu (2002) in one of their publications in 1931, they described the microwave as a radio communication system that inked Dover in the UK and Calais in France. Thus the microwave was viewed as a two way electromagnetic wave. Microwaves are categorised in three different groups depending on their frequencies. They include; 300MHZ to 3GHZ band (Ultra high frequency (UHF)), the 3GHZ to 30GHZ band (Super High Frequency (SHF)) and the 30GHZ to 300GHZ band (Extremely High Frequency (EHF)) (Gupta & Eugene, 2007). The effective nature of microwaves has made the waves be important in the daily use. As a result microwaves have several uses that range from food preparation, Radar detection technology, medical treatment (diathermy) and in the mobile and telecommunications industry. The diverse use of microwaves take advantage of the different properties of microwaves, such as reflection, absorption and transmission. This essay is going to discuss the function of microwaves as used in the preparation of food through the microwave ovens. According to WHO (2005) microwaves are efficient in designing microwave ovens due to their properties as they are reflected by metals and absorbed by non-metals.

Microwave ovens have become a common household appliance in many homes across the world as they overtake the use of stoves and cookers in modern day kitchens. The increased speed of microwaves has made it a preferable cooking appliance among most people, as they cook faster as compared to stoves. This discovery was first made in the 19th century by Percy Spencer, who walked by a microwave source and discovered that the chocolate he had at hand started melting (Marshall Cavendish Corporation, 2003). Thereafter, midsized microwaves were invented and were used in hospitals and military camps for cooking food (Marshall Cavendish Corporation, 2003). Since the 19th century the size of the microwave has drastically reduced from being the size of a refrigerator to the size of a computer. Reinvention and technological innovation has greatly contributed to the improvements made on the microwave since it was first invented. The use of microwaves has also evolved as in modern day homes, people not only use microwave appliances for cooking but also for de-icing frozen foods, heating up cold foods and primary cooking of food (Ishii, 1995). Industries have also adopted the use of microwaves rubber vulcanization and cooking of bacon (Ishii, 1995).

Parts of Microwave Oven

The Electromagnetic Spectrum

A simple diagram of a conventional microwave oven.

Source: Vollmer (2004)

The different parts of a microwave contribute to how the microwave works and its effectiveness. The microwave is made up of several parts which include; the microwave generator, waveguide tube, fan, turntable and the power supply as illustrated in the figure above. However the microwave generator is the most important and essential part of the microwave and the device cannot function without it. The magnetron is the power source of the microwave oven as it supplies the appliance with sufficient microwave electrons. The size and shape of the magnetron will depend on the size of the designed microwave oven, which further explains their varying ratings. For instance, one can find magnetrons with ratings as high as ten million watts. The magnetron is a vacuum tube that consists of an anode and cathode, and its appearance and shape is compared to that of the television tube (Marshall Cavendish Corporation, 2003). The cathode and anode are separated by an accelerating potential, whereby the microwaves are produced by the cathode and are propelled by both magnetic and electric fields (Marshall Cavendish Corporation, 2003).

Vollmer (2004) affirm that the basic domestic microwave used in most homes, are designed with frequencies of around 2450 MHZ with a responding 12.2cm wavelength. Additionally these microwaves intended for domestic use are characterized with magnetrons that have ratings of approximately 750 watts (Marshall Cavendish Corporation, 2003). The microwaves produced by the magnetron are propelled to the cooking chamber which imitate the faraday cage as it is made of metallic walls (Marshall Cavendish Corporation, 2003; Vollmer, 2004). The metallic walls reflect the microwaves produced which in turn take part in cooking the food placed inside the cooking chamber. Vollmer (2004) argue that the existence of antinodes and nodes in the microwave oven, causes some instability in food preparation as this factor tends to make food warmer in some areas while in other it remains uncooked or cold. As a result these microwave ovens have pre-installed turn tables which rotate while the food is inside thus enabling it to evenly cook or heat up by ensuring that the food receives equal amount of energy in all areas. Thus countering the effects caused by nodes and antinodes.

The front side of the microwave oven is made with a glass shield which according to critics endangers the life of users and may lead to microwave energy loss. Therefore as a means to overcome the disadvantages caused by this design, the microwave oven has metal grids that cover the front part (Vollmer, 2004). The metal grids are created with pore like holes which facilitate the deflecting of microwaves and prevent energy loss by reflecting the waves back to the cooking plate (Vollmer, 2004). Additionally, the microwave oven has an automatic door which ensures that the magnetrons switches off as soon as the door is opened for user safety and energy saving purposes. The door also has a fitting quarter-wave choke to counter the possibility of energy loss from the gaps in the door (Marshall Cavendish Corporation, 2003).

How a Microwave Oven works.

The microwave ovens have adopted the use of dielectric heating to achieve its intended purpose. This principle ensures that food is cooked as dielectrics function as electrically polarized elements despite the fact that they are non- conductors of electricity (Marshall Cavendish Corporation, 2003). In instances where the microwave oven is preparing liquid food substances such as water, these materials are able to absorb the microwave energy from the oven and change it to heat (Marshall Cavendish Corporation, 2003; WHO, 2005). As a result the exchange of heat from this two elements, is due to the effectiveness of energy absorption which makes the food particles to vibrate at a high speed. According to Mittal (2005) the amount of energy transferred from the microwave to the food supplements travels at frequencies of about two million hertz (Mittal, 2015). Therefore the rapid movement of food particles causes them to collide against each other and causing a whole plate of food to heat up. Notably, the food molecules are identified as non-conductors of heat but mainly contain ions that respond to electric fields produced by the microwaves hence heating it up due to collision through vibration (Marshall Cavendish Corporation, 2003).

The figures shown below illustrate the behaviours of these ions as they move through the microwave oven. Evidently, one is able to note that these ions have an irregular pattern due to their random movement, as illustrated in fig 1 below. However as they rapidly move they are charged with electromagnetic fields and as a result these ions are further aligned and tend to face one direction as they vibrate as seen in fig 2. By introducing and electrostatic field to this arrangement, contributes to the realignment of charges in the food ions thus rearranging the positive and negative ions redirecting them to face the same direction, as illustrated in fig 3. This arrangement is distorted once the electrostatic field is reversed and the alignment of food ions also reverse as illustrated in fig 4. The continued movement of these food ions due to the effects of the electrostatic fields causes friction and vibration thus leading to a food substance getting heat (Marshall Cavendish Corporation, 2003).

The Electromagnetic Spectrum 1

Fig 1: Random pattern of food ions before being put in an electromagnetic field.

Source: Marshall Cavendish Corporation, 2003

The Electromagnetic Spectrum 2

Fig 2: Aligned pattern of food ions placed in an electromagnetic field.

Source: Marshall Cavendish Corporation, 2003

The Electromagnetic Spectrum 3

Fig 3: Pattern formed by food ions when placed in an electrostatic field.

Source: Marshall Cavendish Corporation, 2003

The Electromagnetic Spectrum 4

Fig 4: Pattern of food ions in a reversed electrostatic field

Source: Marshall Cavendish Corporation, 2003

Therefore one can argue that the generation of heat in a food substance in the microwave oven is due to the rapid movement of microwaves which end up in cooking the food completely. As opposed to other cooking appliances whereby food is heated from the outside surface, the microwave oven heats food from inside through the food ions (Marshall Cavendish Corporation, 2003). As a result some foods when cooked with microwaves will not have the same appearance once cooked with other cooking appliances. Notably, as a precautionary measure while using the microwave oven, users are advised against using metallic appliances in cooking chamber since they tend to reflect away the microwaves resulting to uncooked food. Furthermore the use of metallic cookware may lead to the damage of the magnetrons as it reflects away the microwave energy to it (Mittal, 2015).

The speed with which a food substance cooks or heats up, heavily relies on the molecular structure of this food element and the size of the food particles (Mittal, 2015; Marshall Cavendish Corporation, 2003). Additionally, food substances absorb the microwave energy to a maximum depth of about five centimetres (Marshall Cavendish Corporation, 2003; Mittal, 2015). As a result liquid like food supplements will tend to cook faster as opposed to solid food substances. However, food substances that are more than 5cm in thickness will cook by absorbing heat from the already heated food particles or layers (Marshall Cavendish Corporation, 2003). Users are also advised to wait a few minutes before consuming their food after removing it from the microwave so as to allow heat to penetrate all areas of the food.

The number of advantages of using a microwave oven has surpassed those of other conventional methods of preparing food. One of the main advantages as previously mentioned is the speed. Additionally it is more effective in heating some food substances such as rice if one does not want to change the structure or texture of the food (Marshall Cavendish Corporation, 2003). Like any other thing microwaves have their disadvantages one of them being its inconsistence in preparing some food products such as eggs. This is because the energy from the microwave cooks food from its inside and with the nature of an egg, the energy will make its shell to crack (Marshall Cavendish Corporation, 2003). Additionally the use of microwaves may distort the colour or taste of some food. This is because different foods require different amounts of time to cook as well as different amounts of energy, thus other conventional methods are preferred. Another disadvantage is the fact that microwaves have been identified as health hazards. This is because if a food is not evenly cooked one’s health maybe at risk if he or she consumes it. On the other hand if one uses a faulty microwave oven, this may lead to accidents such as fires or explosions, leading to injuries.

References

Gupta, M. & Eugene, W. (2007). Introduction to Microwaves In M. Gupta & W. Eugene (eds), Microwaves and Metals. New York: John Wiley & Sons (Asia) Pte Ltd, pp.1- 23.

Ishii, T.K. (1995). Handbook of Microwave Technology Applications (Vol. 2), London: Academic Press.

Marshall Cavendish Corporation. (2003). How it Works: Science and Technology (Vol 11). New York: Marshall Cavendish

Mittal, A. (2015). Simply Cooking: Theory and Principles. New York: Anand Mittal Publishers.

Sobol, H. & Tomiyasu, K. (2002). Milestones of Microwaves, IEEE Transactions on Microwave Theory and Techniques, 50(3): 594–611.

Vollmer, M. (2004). Physics of the microwave oven. Physics Education, 39(1): 74-81.

World Health Organization (WHO). (2005). Electromagnetic fields & public health: Microwave Ovens. International EMF Project Information sheet [Accessed on 9http://www.who.int/pehemf/publications/facts/microwaveovens_infosheet.pdf?ua=1. [Online]. Available from: th December 2015]