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Induction cookers: the next generation in cooking?

Induction stoves do not heat up and yet heat the food. The secret lies in the magnetic field

By Dan Yudlevich, Davidson Institute for Science Education website

Induction stoves have become popular in Israel in recent years and are gradually replacing the common gas stoves. The gas burner ignites a continuous stream of flammable cooking gas, and the heat of the combustion heats the cookware resting on the stove. But how does an induction cooker work, which does not heat up at all during its operation, and why are some pots suitable for cooking on them and others not?

Induction, or inspiration in this context, is an abbreviation of the term "Electromagnetic induction", on the basis of which an induction cooker works. In electromagnetic induction, a magnetic field that changes over time induces, that is, produces, electric currents in electric conductors, for example metals, which are close to the source of the magnetic field. The discovery of the phenomenon is attributed to the 19th century English scientist Michael Faraday named after him Faraday's law to inspire. It is true that Faraday discovered the phenomenon in a laboratory experiment, but the Scottish physicist James Clerk Maxwell He formulated its mathematical equations. Maxwell's laws describe the behavior of electric circuits in general and electromagnetic waves in particular.

The electromagnet that creates an electric current

According to Faraday's law, a magnetic field that changes over time induces an electric current in a nearby conductor. The source of the changing magnetic field can be a moving magnet or a magnet that the conductor moves relative to. According to this principle, all electricity generating stations operate - The power plants - except for stations that use solar cells. The source of the magnetic field can also be an electric current flowing in the wire, and if the current changes over time, so does the field it produces. Therefore, an alternating current - a current whose magnitude and direction change cyclically - flowing in the coil, induces a magnetic field that changes over time. The induced magnetic field passes through the air without the need for physical contact between the source of the current and the conductor, and thus a changing current can induce a current in the conductor around it without the need for direct contact between them.

The stove is usually built from a tempered glass surface under which sits a copper wire wrapped in a dense coil. When the familiar is operating, an alternating current flows through the coil back and forth at a frequency of 50-25 kHz (a thousand times per second). This is apparently a high exchange rate, but compared to common radio waves it is a relatively low frequency. Radio, for example, operates at a frequency of about 100 megahertz (a million times per second) and cell phones operate at frequencies of up to five gigahertz (a billion times per second). The alternating current in the coil induces a changing magnetic field in its surroundings, and when a suitable cookware is placed on the stove, the changing magnetic field induces an alternating current of the same frequency at the bottom of the pot or pan.

The heating electromagnet

The cookware heats up due to resistance the metal from which it is made to the electric current that flows through it. The bottom of the vessel needs to conduct electricity in order for enough current to flow through it, but sufficient electrical resistance is required, within a certain range, to generate heat that will heat the vessel and the food inside. To this end, the "crust effect" was harnessed, a phenomenon in which an alternating current flowing in a conductor - for example, the bottom of a pot - does not flow through the entire volume of the metal but only at a certain depth of the surface of the material. The smaller the penetration depth of the current, the greater the resistance of the conductor to the current and it will heat up more. Therefore, tools made of metals with a low penetration depth are suitable for induction cookers. 

Electric vortices are formed in the material, which are machines vapor streams (eddy currents) or eddy currents, and they limit the penetration of the electromagnetic waves. The penetration depth of the alternating current depends on the frequency of the current, and it will decrease the higher the frequency. Theoretically, a frequency as high as possible is better so that the depth of penetration is as small as possible, but induction cookers use a frequency of tens of kilohertz. The working frequency was chosen mainly because of the cost of the components, since components that allow working at high frequencies are much more expensive.

The crust effect also depends on the type of metal, and in particular on the resistance of the material and the magnetic permeability (Permability) His. Metals such as copper and aluminum, which are used to make pots and pans, are good conductors, so the penetration depth in them is small. In contrast, magnetic steel has a permeability a thousand times higher than copper and aluminum, which means that it is magnetized in response to a magnetic field induced in it. As a result, the penetration depth of the current induced in magnetic steel, i.e. the thickness of the "crust" in the crust effect, is sometimes tens of times smaller than the depth of the current induced in copper or aluminum. Therefore, tools suitable for induction cookers are often made of magnetic steel. A convenient rule of thumb to check if a tool is suitable for induction cooking is whether the tool will magnetize to a household magnet.

I have an induction that is more effective

What is better? Induction hob, electric ceramic hob, or gas hob? It depends, among other things, on culinary preferences. Some prefer the traditional style of cooking provided by gas stoves, and we will not deal with this subjective issue. We will focus on issues that can be quantified. Induction has a distinct advantage in energy efficiency, and induction stoves are efficient up to three times gas sellers Induction hobs are also more efficient than standard electric ceramic hobs. This electric stove contains a coil through which a current is passed. Due to the high resistance of the coil it heats up, and in turn it heats the next tool in direct contact with the surface or due to the radiation of the heat produced in the coil. 

Due to the nature of the operation, an induction cooker only consumes electricity if a pot is placed on it, and almost all the electricity is invested directly in heating the cookware. A gas stove, on the other hand, produces heat by combustion, and therefore a lot of energy is wasted heating the cooking environment. This is also the explanation why induction stoves often also heat up dishes faster than gas stoves.

In general, induction cookers are safer to use. Safety mechanisms cut off the current if a suitable utensil is not resting on the stove, and there is no danger of burns directly from the heating source because the coil cannot directly heat our body. Of course there is a risk of burns from hot cookware or if the stove is still hot after cooking, similar to a gas stove. A ceramic electric stove is dangerous in this respect as it heats up the surface very much and sometimes this cannot be noticed, compared to a gas stove where you can see the burning flame. Gas leakage is a significant danger in gas systems, and it does not exist in a high level that is based on electricity, although gas leaks are rare in standard and modern infrastructures and occur mainly in improvised and unsupervised infrastructures. 

Induction cookers produce electromagnetic radiation, but the frequency range of the radiation It is considered safe and anyway most of the radiation is absorbed by the cookware. Induction cooks there is no risk of electric shock despite the fact that the induction cooktop induces a current at the bottom of the pot. The current is induced in a very small range at the bottom of the wall, therefore no current flows in the area of ​​the pot handles, and the current at the bottom stops as soon as the pot is lifted. At least the electric current "prefers" to flow in the pot, because in the pot the resistance is lower than the resistance of our body. If so, the main danger with induction cooktops is the risk of burns from a hot pot and not the risk of electrocution.

The induction pays off

During a power outage, there is an advantage in the availability of a cooking and heating source that does not depend on electricity. However, this advantage was relevant when the electricity grid in Israel was less reliable, whereas today the electricity grid in Israel is one of the most reliable in the world. In recent years There were about 200 minutes of power outage per customer per year, on average, less than 0.05% of the electricity supply. This figure means that the reliability of the electricity supply is over 99.95 percent. In one respect, gas stoves have a distinct advantage even today, and that is the cost of the initial investment. Basic induction cooker models cost two to three times more than gas cookers. Although, According to analysis According to the Department of Energy, this cost is offset by the high consumption costs of domestic gas, making induction cooktops cheaper in the long run.

In conclusion, induction-based stoves are an innovative mechanism for home cooking, and their popularity is increasing. Their mechanism of action is based on the induction of electromagnetic fields that directly heat cookware made of magnetic metal. Induction stoves are considered safer than gas stoves, they are also much more efficient, and their distribution is expected to increase in the coming years.

For the article on the Davidson Institute website

To the Davidson Institute for Science Education website

More of the topic in Hayadan:

8 תגובות

  1. Maybe in Shigra you can count on a normal power supply, but those who don't want to depend on Nasrallah or Khamenei to drink coffee need some kind of non-electric backup.

  2. Reply to Shtoin:
    It was definitely written in the article.
    a quote:
    "Of course there is a risk of burns from hot cooking utensils or if the stove is still hot after cooking, similar to gas cooking"

  3. From many years of experience as induction cooks, they are indeed heated by secondary heating from the pot, but several orders of magnitude less familiar with electric ceramics that heat up and light up their surroundings from excessive heat, or gas stoves in which the tripod ignites at hundreds of degrees from the visible fire, on the other hand, the heating from an induction pot does not reach extreme temperatures, as Try putting a piece of paper under an induction cooker pot and you'll see that it doesn't burn at all.

  4. The attached image was created by artificial intelligence and of course contains a lot of errors. Below any criticism, and not at your usual level!

  5. To the best of my recollection, modern induction stoves require a three-phase electrical system, which although most houses have as standard, but not always in the old houses.

  6. The main thing is that we were told that the gas rates dropped a lot after the start of gas production from the 'Karish', 'Tamar' and 'Levitan' fields.

  7. It is evident that the learned writer has never cooked on an induction stove. Theoretically they do not heat up, but the cooking pots do heat up and consequently, heat up the stove. Therefore, the stove itself boils after cooking and its cooling rate does not fall below the cooling rate of a stove that operates on an open flame.

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