Microwave Ovens

 

A
microwave oven is a kitchen appliance that cooks food by heating using microwaves.                                                                                                
   

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What
are microwaves?

Microwaves
are a form of electromagnetic energy and are part of the electromagnetic
spectrum, just like light waves. They are the shortest type of radio waves. They
can travel over long distances and they carry a lot of energy, so they have a
range of applications, such as in TV broadcasting,
radar for air and sea navigation, and telecommunications including mobile phones. The microwaves that are used to cook
and heat food in microwave ovens are usually about 12 cm long and have a
frequency of 2.4GHz.

What is the science behind microwave ovens?

 

Microwaves are reflected, transmitted or absorbed by
materials in their path. Metallic materials reflect microwaves while
non-metallic materials such as glass and some plastics are mostly transparent
to microwaves and transmit them. Materials containing water such as
foods, fluids or tissues, readily absorb microwave energy.

The main component of a microwave oven is the magnetron
which is a vacuum tube that generates microwaves by bouncing electrons around
inside a vacuum filled cavity that is exposed to a strong magnetic field,
causing the electrons to absorb energy and eventually, the energy is released
as microwaves. Generating microwaves requires a very high voltage that is usually
more than a thousand volts that
is generated from a 120-230 V wall outlet using a transformer. The
microwave radiation is gathered and directed into the cooking space of the
microwave by a device called a wave guide. The cooking space is a metal-lined
box. The metal walls reflect the microwaves and they bounce around until they hit
the food. The water molecules in the food absorb the radiation, get excited, move
faster and the friction between the molecules results in heating which cooks the
food.

The reflection of microwaves against the metal walls
produces peaks with lots of microwaves, and troughs with few microwaves; this
is called a standing wave. The microwave has a rotating dish in it to make sure
that none of the food is sitting in a trough on this pattern and not getting
heated. A grid of wires inside the door prevents the microwaves from escaping.

There is also a cooling fan that prevents the inside of
the oven from getting too hot.

Who
invented the microwave oven?

Microwave
ovens were an accidental invention in the 1950s, when the main use for
magnetrons was in radar, which was a way of using radio waves to help airplanes
and ships find their way in the night or in poor weather. Percy Spencer was an
American electrical engineer who was trying out some experiments using a magnetron at the Raytheon
Manufacturing Company. One day, he found that a chocolate bar that was in his
pocket had melted because of the heat from the magnetron. He realized that a
magnetron could be used to cook food. After he successfully cooked some
popcorn, he realized that he could develop a microwave oven with a magnetron as
its main component for cooking all types of food.

 

What
are the advantages of microwave ovens?

·      
Microwave energy
penetrates deeper into the food and reduces the time for heat to be conducted
throughout the food, reducing the overall cooking time.

·      
Food
up to a depth of 1.5 inches is cooked uniformly in a microwave oven.

·      
Microwave
oven cooking is healthier because it does not require oil.

·      
It
is quicker to thaw frozen food in microwave ovens when compared to allowing the
food to thaw at room temperature.

·      
Cooking
in microwave ovens minimizes the loss of nutrients in food as compared to
cooking in pressure cookers.

·      
The
cooking time in microwave ovens is one-fourth of the time taken on gas stoves.

·      
They
save energy since they don’t require preheating unlike conventional ovens.

·      
Microwave
ovens work on electricity, so it is free of the pollution associated with
fumes.

·      
Microwaves do
not directly heat the food containers; they usually get warm from being in contact
with the hot food, so
even children can cook safely with microwave ovens.

 

What
are the disadvantages and problems with microwave ovens?

·      
The
color, texture and taste of food is often changed.

·      
Leaky
microwave ovens can be hazardous to health because prolonged exposure to
microwave radiation can cause damage to living cells and tissues because the microwave energy can be absorbed by the body
and produce heat in exposed tissues. This is especially a problem in organs
with poor blood supply and temperature control, such as the eye, or
temperature-sensitive tissue like the testes.

·      
Burn injuries
can result from handling hot items heated in a microwave oven. Boiling
water on a conventional stove allows steam to escape through bubbling action as
the water begins to boil. In a microwave oven there may be no bubbles, but the
water can super-heat and may suddenly boil by a single bubble or just by
putting a spoon into it.

·      
Certain items
with non-porous surfaces or composed of materials that heat at different rates
(e.g. yolk and white of eggs) can heat unevenly and may explode.

·      
Food heated in a
microwave oven should rest for several minutes after cooking is completed to
allow the heat to distribute throughout the food.

·      
The
penetration depth of the microwaves in microwave ovens is only up to 1.5
inches. Food that is thicker than 1.5 inches cannot be cooked evenly, it must
be stirred or cooked slowly on low power to allow the heat to conduct to the
center and to ensure uniformity.

·      
Uneven cooking
in a microwave oven can lead to a health risk if parts of the food are not
heated sufficiently to kill dangerous micro-organisms.

·      
Only
microwaveable utensils such as ceramic and glass can be used in microwave ovens.
Metal containers can produce dangerous sparking. Plastics may
melt or burst into flames if overheated.

Why
can’t metal and plastic containers be used in microwave ovens?

Metal containers
will work as antennae and generate an electric current or create an electric
arc. Plastic containers will get heated and the molecules will get into the
food, and plastic residues in the food are unhealthy and unsafe.

 

What
was the impact of microwave ovens on society?

At the start of the 20th
century, cooking was done on iron stoves with coal and wood as the energy
sources. Now that microwave ovens have been invented, a lot of energy is saved,
and we no longer depend on fossil fuels to provide energy. Microwave ovens can
also cook and heat food faster than gas stoves.

 

Fun
facts about microwave ovens

·    
The first microwave oven was 6 feet in height and weighed about
750 pounds. It used three times as much power as the microwave ovens today, and
was water-cooled.

·    
When microwave ovens were first introduced, most people did not
buy them because they cost over $5000.

·    
The
first food that was cooked intentionally was popcorn.

·    
Over
90% of all American households have microwave ovens.

·    
It
is a common misconception that food in a microwave oven gets cooked from the
inside, microwave ovens actually cook food from the outside inward.

·    
NASA
uses the same microwave technology that is in microwave ovens for communication
in space.

·    
Before
they became known as microwave ovens, they were called electric ovens.

·    
Exposure
to microwave radiation from ovens has not been proven to cause cancer as
alleged.