thermodynamics

Microwave Oven

Microwave Oven is an electronic device. It uses microwave radiation to heat and cook food. The microwave has a wavelength range of 0.1 cm to 100 cm. A microwave oven uses a microwave with a wavelength of around 12 cm.

Magnetron

Magnetron comes from 2 words- magnet and electron. It is also an electronic device. It produces microwave by using the interaction between a flow of electrons and a magnetic field. Actually, it is the heart of a microwave oven.

How Microwave Oven Works

Microwave oven

At first, when the oven is turned on, the control board sends a voltage of 120V to the thermostat. It sends the voltage of alternating current to the primary winding of a transformer. By electromagnetic induction, primary winding produces sufficient voltage to the secondary winding. After that, the capacitor sends the voltage needed to the magnetron.

How Magnetron Works …

magnetron inside visualization

Magnetron works by creating an electric field and a magnetic field.

  • A cathode and an anode produces the electric field. It helps to throw out the electrons. There are a copper rod and a copper ring in the magnetron. A thorium-tungsten filament coils around the rod. Thorium is a good source of electrons. Tungsten has a very high boiling temperature. So, this filament is used as cathode– negatively charged electrode. The copper ring is the anode– positively charged electrode. When the magnetron gets the voltage, cathode becomes very hot and releases electrons. The name of this type of emission is thermionic emission. So, the electrons move towards the anode.
  • There are two magnets in a joint with the copper ring. Because of the magnetic field force, the electrons turn their direction. As a result, electrons start rolling around the filament in the vacuum of the ring.

How the Microwave is Produced

Consider two electrons from the electrons emitted. The first electron gets an electric field force and tries to go to the anode through a particular cavity. But because of a magnetic field, the electron faces another force. So, the electron gets back perpendicularly and turn around the filament. Then the second electron gets into the place of first electron. Similarly, It faces the same forces and turns. Then another electron comes. This continuous movement of electrons makes a resonance in a cavity. All the electrons move at a specific frequency. This frequency is equal to the microwave frequency. Every electromagnetic radiation has an electric and magnetic field perpendicularly. As both fields present there, there will be microwave radiation.

N.B: Resonance is an incident in which an external force drives another system to oscillate with higher amplitude at a constant frequency.

How Oven sends the Microwave into the cooking compartment

An antenna is connected to the copper ring cavity. It delivers the microwave to a kind of funnel called waveguide. The waveguide guides the wave to the cooking compartment.

How Microwave Cooks Food

Water, fat, sugar etc. can absorb microwave. When microwave penetrates the food, it vibrates the molecules. This vibration produces friction between molecules. So, The friction produces heat. The cooking compartment is lined with metal. Because metal reflects microwave. So, the waves continuously bounce around the metal until food absorbs them. The food is placed on a turntable. So, microwaves can heat up all the portion of food equally. In this process, microwave cooks food.

Keynotes:

  • A Conventional oven cooks food by heating the air inside the cooking compartment. Food gets the heat from the air by conduction process. So, there is a possibility that, heat cooks outside of the food well, but inside of food remains uncooked. But microwave oven uses the microwave that penetrates the food. So, we can cook food perfectly in a minimum time.
  • Microwave can cook the food easily whose thickness is around 1 inch or less. But microwave can not penetrate more than that thickness. Because it loses energy wiith penetration.
  • Thermionic emission is a flow of charge where high temperature cases charges to be excited and released.

For any information, please comment. Thank you !!!

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