How Does a Microwave Work

Microwave oven side removed, magnetron visible

How does a microwave work? you ask. You put the food in the microwave oven, set the timer, press start, wait a few minutes and “Ping!” – the food’s piping hot. How can the food cooked in the microwave be so hot yet the inside of the microwave oven stay so cool? The microwave oven is electric, so there is  no flame. So how comes there’s no orange, glowing electric element to produce the heat? And how does the microwave oven heat the food so quickly? What kind of witchcraft is going on in there?

These questions about how microwave ovens work are asked all the time, simply because most of us are used to cooking with conventional ovens. Conventional ovens heat food with a hot gas flame or an electric element which produce electromagnetic waves that heat everything inside the oven, including the air. These types of waves are called infra-red waves. As these waves move through the oven, the space inside of the oven becomes hot and begins to heat the surface of the food. The heat eventually travels through to the centre of the food and after some time the food becomes cooked.

Like conventional ovens, microwave ovens work by producing electromagnetic waves. The waves are called microwaves and are of course what give microwave ovens their name. Different types of waves behave differently because they come in different lengths. Microwave wavelengths fall between those of the tiny infra-red waves used in conventional ovens and the much longer FM radio waves which broadcast your favourite music to your car stereo.

Wave Type Size in cm Similar Size Frequency
Microwave 12.23 cm Average woman’s foot 2.45 GHz
Infra-red 700 nm – 1 mm Human hair width 430 THz – 300 GHz
FM Radio wave 3.4 m African elephant length 100 MHz

The picture below shows all of the different types of electromagnetic waves relative to one another, starting with the longest waves on the left, to the shortest on the right.

electromagnetic wave chart

 

The conventional oven uses a gas flame or electric elements to produce infra-red waves which heats both the food and the air around the food. The microwave oven uses a device called a magnetron to produce microwaves which are directed to the inside of the microwave oven via a tube called a wave guide. The microwaves bounce around inside the microwave oven until they hit water, sugar or fat molecules in the food. 

cutaway microwave oven diagram

 

Every 2.45 billionths of a second, the magnetron tube emits a microwave. Each microwave alternates between a positive and negative charge. This rapid switching causes the water, sugar or fat molecules in the food to repeatedly spin around to the opposite polarity a bit like how the needle of a compass would flick from north to south if you kept passing a magnet back and forth across the face of the compass.

The molecules spinning at the ultra high speed of 2.45 GHz (2.45 billion times per second) continuously rub against one another causing friction which makes them hot. So kind of like the way radio waves transmit music which makes people dance, making them get all hot and sweaty, microwaves make molecules dance a crazy, frantic spinning dance with a lot of rubbing or friction causing them to get hot.This is the heat which cooks or warms your food.

microwave makes water molecules spin causing friction
Two water molecules affected by microwaves spin causing heat through friction. Each water molecule is made up of a Hydrogen atom (blue) and 2 Oxygen atoms (red) thus H2O

animated shakira waka-waka dance

Shakira and her dance crew looking extremely hot due to rapid waist polarity switching while doing the waka-waka. Note the similarity to the motion of  the water molecules above.Microwaves are not able to escape from the oven since they are reflected off the metal walls inside the oven. You’ll also notice that the door which is usually made of glass or plastic has a metal mesh covering it. The holes in the mesh are wide enough to let you see through them but are too small to allow microwaves to escape.

Hopefully that will explain things to you so if anyone ever asks you how does a microwave work? you can tell them exactly how.

Microwave Oven facts from NEFF

EFFICIENCY

ENERGY
Microwaves only use about 1Kw
of energy per hour compared to
5kW in many conventional ovens.

TIME
Microwave ovens will save time in
the kitchen. If you need to
defrost something quickly or
speed cook a dinner course
they’re the ideal solution

 

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4 thoughts on “How Does a Microwave Work

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