How do microwave ovens work?

Microwaves work almost like magic. They cook food without external heat and with good regularity compared to traditional methods. Despite its benefits, however, some are nervous about the health hazards of electromagnetic waves. Can microwaves cause harm? Let's find the answers to the questions in this article.

You may be surprised to read that the discovery of the microwave oven was accidental.

Magnetron

Researcher Percy Spencer conducted tests on a device called a magnetron. The magnetrons generated strong microwave radiation during the experiment. He found that the candy bar in his pocket had completely melted while trying to investigate the use of microwaves in cooking food.

This experiment showed that a high-power microwave is capable of cooking food, but of course, the question is what melted the candy in the microwave. Microwaves are electromagnetic waves in a specific spectrum. Like any other electromagnetic wave, they have oscillating electric and magnetic fields. The oscillating electric field component of the electromagnetic wave is responsible for producing heat. Now let's see how these oscillating electric fields produce heat.

The food we eat contains most of the water. Water is a polar molecule. The hydrogen atoms

Polar molecule of water

of the water, molecules are arranged at an angle of 105 degrees to each other and both the hydrogen and oxygen atoms are charged. The water molecule behaves like a dipole. When an electric field is applied to the water molecule, it begins to rotate due to the torque generated at the dipole. In electromagnetic waves, the electric field oscillates continuously, and the water molecules continue to oscillate. This oscillating rotation causes the molecules to rub against each other, creating friction and heat in the food. Now let's see how this heat generation concept can be translated into a viable model. In order to use the energy of electromagnetic waves efficiently, it has to be reused several times. An efficient way to achieve this is to reflect and confine it to a specific area.

The best way to make this reflector is with the help of metal. The metal surface causes microwaves to reflect off its surface, and if you hold another reflector on the source side, the reflection will continue. In this way, one can capture the energy of electromagnetic radiation within a chamber However, the most efficient way to capture the energy of electromagnetic waves is to use a technique called a resonant cavity. In this way, the intensity of electromagnetic waves also increases.

Let's understand the concept of the resonant cavity using a simplified standing wave approach. A standing wave is a standing wave that varies in time but does not propagate in space. You can understand how a standing wave differs from a normal traveling wave. It occurs when two waves of equal amplitude and frequency, propagating in opposite directions, are superimposed on each other. You can understand that the waves have phase differences of 180. If you add both electromagnetic waves here, they cancel each other out perfectly.

The result is a larger sine wave. Here you get an even larger sine wave as the output. By

Standing wave

comparing the results of these three instances, it becomes clear that the resulting electromagnetic wave only oscillates in its position without propagation.

Let's explore a practical way to create two opposing traveling waves. We will get a clear solution to this when we understand how electromagnetic waves are reflected from a metal surface. We know that when a wave hits a reflector, it returns to its source. Can you find a correlation between this reflected wave and the incident wave? The reflected wave is actually the wave that would have traveled forward if reflectors are not placed.

First, of course, you need to fold these imaginary parts 180 degrees. Now this time we add

Incident and second reflected wave

another reflector to the side of the source, this will again reflect in the same way and create a third wave and this process will repeat. However, if you hold the second reflector at the intersection of the first and second waves, the third wave is created. After that, the reflection is the same as the first wave.

This is a clever solution. Placing the second reflector this way we only see two waves traveling in opposite directions instead of lots of reflected waves. If you find out the result of this, it will be a standing wave. It is known that standing waves arise when the distance between the source and the reflector is an integral multiple of half the wavelength.

Therefore, the dimensions of the closed structure are determined by the wavelength of these waves. A fun fact now is to measure the cavity length of the microwave oven in your kitchen. It will be an integer multiple of that wavelength.

It is apparent from this visible that some points of the standing wave are at high energy intensity and some others are at zero intensity. Due to this, there might be many spots in a microwave a few are cold than others. Just put the shredded cheese inside your microwave oven for one minute. What you spot after one minute is the cheese floor with some warm

Cheese with hot and cold spots

spots. The presence of such warm spots reasons a microwave to prepare dinner meals unevenly. In short, the cavity resonance approach we use to trap microwaves extra efficaciously has brought about the introduction of cold and warm spots. To triumph over this trouble in recent times, a microwave includes a rotating plate that allows the meals to warm evenly. The device responsible for generating microwaves is called a magnetron. A magnetron emits microwaves in all directions. To confine the wave to propagate in a chamber the magnetron is hooked up to the waveguide. From the waveguide, the waves come into the cooking chamber to warm meals.

Another query that needs to be responded to is whether or not microwaves are the most effective electromagnetic waves able to heat food or if there are other methods that might accomplish the identical result. The solution is that any electromagnetic waves have the ability to warm however they arrive with definite limitations. Waves with large wavelengths can without difficulty pass through the food in order that they may not be capable of producing plenty strength to it additionally. To get a standing wave, larger devices may be required. Shorter wavelength waves are absorbed extra swiftly at the outer floor of the food. So they do not penetrate far enough inside the food to cook it even if we want to cook deeply. So we have to apply high power that might be unfeasible withinside the microwave range. The appropriate frequency for all realistic functions and which did now no longer require a license become 2.45 GHz. The effective microwaves produced with the aid of using an oven may be dangerous to human beings if we are available in direct touch with them. But do not worry the electromagnetic radiation produced with the aid of using a microwave oven is usually constrained inside it. It will by no means go away from the chamber so there's no factor in disturbing approximately the fitness dangers because of the electromagnetic radiation of microwave ovens.

Now the most query is why heating with a microwave oven is superior to traditional heating strategies. Since microwaves can penetrate that food. The meals are cooked from the inside slowly than cooking on the outer side. Moreover, it cooks food quicker than different traditional strategies. The traditional method cooks food from the outside in as opposed to the inside out. This is because the heat energy has to travel from outside to inside but this method can be useful on some occasions when you need food with a crisp surface and a soft interior or baking the traditional heating method is preferred. Due to this reason, modern microwave ovens come with a traditional option for cooking purposes. We hope you got a complete understanding of the physics behind microwave ovens. 

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