How does Microwave oven work?
Microwave ovens function almost magically, cooking your food without using any external heat and with better consistency than traditional techniques. But how do they do it, and despite their benefits, some people are concerned about health risks from electromagnetic radiation. Will microwaves harm you? All of these questions will be answered. In this post, we’ll look at how a microwave oven works. So, let’s get started.
It may surprise you to discover that the microwave oven was invented by accident while scientist Percy Spencer was experimenting with a gadget called a magnetron.
What is Magnetrons?
Magnetrons produce a lot of microwave radiation. During the experiment, he saw that the candy bar in his pocket had totally melted, and it occurred to him to investigate the use of microwaves in food preparation.
This experiment revealed that a high-powered mobile microwave can heat food, but it also raises the question of how safe it is to use.
What was in the microwave that melted the candy bar?
Microwaves are electromagnetic waves that have oscillating electric and magnetic fields, just like any other electromagnetic wave. If you track the amplitude of the wave in a specific area, you can see this oscillation. In the case of the chocolate melting accident, the oscillating electric field component of the electromagnetic wave is responsible for cooking the food.
Now let’s see How these oscillating electric fields cook food?
Most of the food we eat contains water, which is a polar molecule with hydrogen atoms arranged at an angle of 104 degrees from each other and charges on both hydrogen and oxygen atoms, causing the water molecule to behave like a dipole.
When an electric field is applied to a water molecule, it begins to rotate due to the torque produced on the dipole. Because the electric field in electromagnetic waves oscillates continuously, the water molecules will continue to oscillate. As the molecules rub against each other, friction and heat are produced in the food.
Now let’s look at how to convert this heat generation concept into a workable product?
The easiest way to achieve this is to reflect the electromagnetic wave and keep it restricted in a specific area. The ideal approach to make this reflector is with the help of metal, as the metallic surface causes the microwave to reflect from its surface, and if you keep another reflector at the source site.
We will be able to trap the energy of electromagnetic radiation within a volume if the reflection continues; nevertheless, the most efficient means of capturing electromagnetic wave energy is through the use of a technology known as a resonance cavity.
What is a resonance cavity?
This method also raises the intensity of electromagnetic waves. Let’s look at the concept of a resonance cavity using a simpler standing wave approach. A standing wave is a stationary wave that fluctuates in time but does not travel in space. You can comprehend what a standing wave is by looking at these two wave animations.
How a standing wave is different from a normal traveling wave it is formed?
Examine these two electromagnetic waves that are traveling in different directions and are overlaid on each other when their amplitude and frequency are the same and they are flowing in opposite directions.
- You can see that the waves have 180 phase discrepancies here, which means that when you combine both electromagnetic waves, they will cancel out precisely.
- As a result, the sinusoidal curve becomes larger.
- By comparing the results of these three instances, it is evident that the resultant electromagnetic wave just oscillates in its place without traveling.
How to produce two oppositely traveling waves practically?
We will have a clear answer if we understand how electromagnetic waves are reflected on a metal surface. We know that when a wave encounters a reflector, it returns to its source. Can you see any link between the reflected and incident waves? The reflected wave is the wave that would have traveled forward if there had been no reflector. Of course, this imaginary part must be folded 180 degrees as illustrated.
Now add the third reflector to the side of the source, which will reflect the same way as the first and second waves and form the third wave, and the process will repeat. If you maintain the second reflector at the intersection point of the first and second waves, the process will not repeat.
Following the reflection, the third wave will be identical to the first wave. This is a creative setup because instead of many reflected waves and confusion, we will only witness two waves flowing in opposing directions if the second reflector is placed in this manner.
Standing waves are formed when the distance between the source and the reflector is an integer multiple of half-wavelength, and the wavelength of these waves determines the dimensions of the closed structure.
Now here’s a fun fact: the cavity length of your microwave oven in your kitchen will be an integer multiple of this wavelength. It’s evident from this diagram that some locations of the standing wave have significant energy intensity while others have none.
As a result, there would be many cold and hot areas in a microwave. Using cheese, you may illustrate these cold and hot places in your kitchen’s microwave oven by keeping the shredded cheese inside for one minute.
What you see after one minute is the cheese surface with a few hot spots?
The presence of such hot spots causes a microwave to cook food unevenly. In short, the cavity resonance technique we use to trap microwaves more efficiently has resulted in the creation of cold and hot spots. To overcome this problem, today’s microwaves have a rotating plate that helps the food cook evenly. The component responsible for producing microwaves is known as a magnetron.
A magnetron emits microwaves in all directions to confine the wave to one dimension of propagation. The magnetron is connected to the waveguide, and the waves enter the cooking chamber to heat the meal. Another question that needs to be addressed is the following:
Whether microwaves are the only electromagnetic waves capable of heating food or if there are any other ways that could accomplish the same result?
Any electromagnetic pulse has the ability to heat food, but it has several restrictions. Long-wavelength waves can easily pass through our food, so they won’t be able to transfer much energy to it. Additionally, large devices will be required to get a standing wave. Short wavelength waves are absorbed more quickly on the food’s outer surface, so they don’t penetrate far enough down to cook it evenly. If we want to cook deeply, we’ll need to switch to a very high power source.
2.45 gigahertz was a sufficient frequency for all practical uses that did not require a license. The powerful microwaves produced by an oven can be harmful to humans if we come into direct contact with them, but don’t worry because the electromagnetic radiation produced by a microwave oven is always contained within it and never leaves the chamber, so there’s no need to be concerned about the health risks posed by microwave oven electromagnetic radiation. Now for the most interesting question.
Why is heating with a microwave oven superior to conventional heating methods?
Because microwaves can enter the food, it is cooked from the inside out, slowly cooking on the surface, and it cooks food faster than other techniques. Because heat energy must flow from outside to inside, the convection method cooks food from the outside in rather than the inside out. However, this approach can be effective on occasion when you need food with a crisp exterior and a soft interior, especially for baking.
Because the convection heating method is preferable, modern microwave ovens include a convection option for baking. We hope you now have a thorough understanding of microwave oven physics.
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