E.M.G. YADAVA WOMEN’S COLLEGE, MADURAI-14
(An Autonomous Institution – Affiliated to Madurai Kamaraj University)
Re-accredited (3rd Cycle) with Grade A+ and CGPA 3.51 by NAAC
THE PHYSICS OF HOUSEHOLD APPLIANCES
MICROWAVE OVEN
Mrs.R.Kayalvizhi, Head & Assistant Professor
Miss K.Ramya, Assistant Professor
Department of Physics
E.M.G Yadava Women’s College, Madurai

A Microwave oven is a kitchen appliance that heats and
cooks food.
Microwave ovens convert electrical energy into a
form of electromagnetic radiation called microwaves.

What are microwaves?
em spectrum
• Microwaves are a form of electromagnetic energy,
like light waves or radio waves.
1.
• Used in communications such as to relay long-distance
telephone signals, television programs and computer
information across the earth or to a satellite in space,
radars and in detecting speeding cars
2.
• Microwave has become most familiar as the energy
source for cooking food
3.

Contd...
1.
• All microwaves use a timer for the cooking time, at the end
of cooking time, the oven switches itself off.
• Microwave ovens heat food without getting hot themselves.
2.
• A 2006 study found that microwaving wet sponges for two
minutes (at 1000 watt power) removed 99% of coliforms,
E. coli and MS2 phases.
3.
• So, microwaves oven are great to use.

History of Oven
• It was Invented accidentally by Dr. Percy Spencer
in 1945.
• While testing a magnetron during work, he
discovered the candy bar in his pocket melted.
1.
• Experimented with other food products (popcorn and
eggs), and realized microwaves can cook foods quickly.
• At 1947, 1st commercial microwave oven produced
(called Radarange)- Mostly used by restaurants,
railroad cars, ocean liners and military.
2.
• Improvement and refinements made by 1967, 1st
domestic microwave oven produced.
• By 1975 sales of microwave ovens exceeded that of
Gas Ranges.
3.

Microwave oven : early days.
1.
• The first microwave oven was priced at $2,000.00 to $3,000.00.
2.
• Mostly used by restaurants, railroad cars, ocean liners and military.
• In 1980, it becomes necessity for every home maker.
3.
• In 1976, the microwave oven became a more commonly owned
kitchen appliance. Microwave oven by now.
4.
• Microwave ovens heat food without getting hot themselves.

Technical Design
Basic design of a Microwave oven.
• A transformer
• a magnetron
• a stirrer, a waveguide
1.
• A control panel is located on the external
casing where oven cavity is normally
bolted.
2.
• There is a front panel on the oven body by
which user can control/program the machine.
3.

Basic design of Microwave Oven

A Magnetron: Here the yellow part in the middle is cathode and the surrounding
bronze part is anode.
Magnetron
•Magnetron is a high-powered vacuum tube which generates
microwave.
•It’s a diode type electron tube.
 •There’s a cathode at the center of a magnetron.
A ring shaped anode surrounds the cathode.

Magnetron
WAVEGUIDE
• A waveguide is a structure that guides microwaves.
• Generally waveguide is made of brass, copper, silver,
aluminium, or any metal that has low bulk resistivity.
STIRRER
• Looks like a fan.
• Usually situated at the top of the cavity.
• Moves the microwaves around the cavity.

Main chassis
 This is the place where every parts of a oven is organized
 The main chassis is placed on the pallet, and the cavity is screwed on to
the chassis.
 And the door is attached next to the cavity.
 A front panel that allows the operator to select the various settings and
features available for cooking is attached to the chassis.

A Schematic diagram of oven

How do microwaves cook food?
1. Inside the strong metal box, there is a
microwave generator called a magnetron.
When you start cooking, the magnetron
takes electricity from the power outlet and
converts it into high-powered, 12cm (4.7
inch) radio waves.
2. The magnetron blasts these waves into the
food compartment through a channel called a
wave guide.
3. The food sits on a turntable, spinning slowly
round so the microwaves cook it evenly.

Contd..
4. The microwaves bounce back and forth off the reflective metal walls of the food
compartment, just like light bounces off a mirror. When the microwaves reach
the food itself, they don't simply bounce off. Just as radio waves can pass
straight through the walls of your house, so microwaves penetrate inside the
food. As they travel through it, they make the molecules inside it vibrate more
quickly.
5. Vibrating molecules have heat so, the faster the molecules vibrate, the hotter the
food becomes. Thus the microwaves pass their energy onto the molecules in the
food, rapidly heating it up.

Types of Oven
There are three types of microwave ovens:
1. Solo 2. Grill and 3.Convection.
Solo microwaves are considered basic or entry level.
A solo microwave is a basic/ entry level microwave designed to reheat food
and beverages, cook noodles, and defrost frozen foods.
Solo microwaves use electromagnetic radiation to cook food and drinks.
Solo microwave ovens can be used in both commercial and domestic
kitchens.
These microwave use watts to convert energy into heat, which then cooks
the food.
Grill microwaves are considered the next step up:
A grill microwave is a microwave that gives families the grill taste without
needing to fire up an outdoor grill.
A grill microwave oven can do everything a solo microwave can do plus
grill pizza, chicken, and fish.

Contd...
Convection microwaves are at the top. The main difference between the
three are the included features, watts, and price.
Convection microwave ovens include all of the cooking options of solo and
grill microwaves and have the ability to bake foods. The convection
microwave uses a different heater and fan combination to cook all of the
foods listed plus more.
Solo and grill microwaves use metal boxes to direct watts toward the food
to cook. Convection microwaves, on the other hand, pushes heat through
the microwave using a fan which creates a better cooking environment.

It saves time and energy.
It is safer than general fuel stoves.
Taste of the foods remain same.
If properly used, microwave cooking does not affect the nutrient
content of foods.
Reduces the consumption of oil.
Advantages of Microwave Oven

Health Hazards
 Microwave radiation can heat body tissue the same way it heats food.
 Exposure to high levels of microwaves can cause a painful burn.
 Microwave oven used low level of microwaves, within the region of non-
ionizing radiation.
 Microwaving converts vitamin B12 from an active to inactive form.
 Still uncertain in the effects of humans from long term exposure to low
level of microwaves.

Maintenance of Oven
• Step 1: Fill a bowl with 2 cups of water and 4 tablespoons of vinegar.
• Step 2: Add a toothpick to prevent boiling over.
• Step 3: Microwave the bowl for five minutes.
• Step 4: Let the bowl sit for three minutes.
• Step 5: Wipe the microwave down with a sponge.

Preventive Maintenance
 Use microwaveable containers. Non-microwaveable plastic containers can melt and
even leave toxic particles in your food. Make sure you use containers that are
specifically labelled as microwave-safe. These are often made of ceramic, glass, or
tougher plastic.
 Cover your food. Use a microwave-safe plastic cover over your dishes or use the lids
on your microwave-safe food containers. Splashes happen during the microwaving
process as the liquid heats up, and preventing them from hitting the walls of the
microwave makes cleanup easier and protects the paint and metal of the oven.
 Never put metal in your microwave. The microwaves emitted from the oven
bounce off of metallic materials, so metal in the oven will cause the interior to heat
up unevenly and can cause damage. This includes aluminum.
 Make sure the door closes properly. If the door is damaged or the seal is cracked,
food won’t cook evenly and radiation can escape.

Conclusion
 The microwave oven was a very beneficial inventions that has make life
easier for people everywhere all over the world.
 Even though the microwave was invented a very long time ago it is still
used toady and is still being improved by technology.

References
1."Microwave cooking and nutrition". Family Health Guide. Harvard Medical School. 6 February
2019. Archived from the original on 17 July 2011. Retrieved 13 April 2021.
2. Pitchai, K. (2011). 'Electromagnetic and Heat Transfer Modeling of Microwave Heating in
Domestic Ovens' (Unpublished master's thesis). University of Nebraska at Lincoln. Retrieved
August 28, 2020
3. "Microwave Technology Penetration Depths". pueschner.com. Püschner GMBH + CO KG
MicrowavePowerSystems. Retrieved 1 June 2018.
4.Health, Center for Devices and Radiological (12 December 2017). "Resources for You
(Radiation-Emitting Products) - Microwave Oven Radiation". fda.gov. U.S. Food and Drug
Administration. Retrieved 1 June 2018.
5. "Microwave Oven". Encyclopedia Britannica. 26 October 2018. Retrieved 19 January2019.
6. Gallawa, John Carlton (1998). "The History of the Microwave Oven". Archived from the
original on 31 May 2013.
7. Datta, A. K.; Rakesh, V. (2013). "Principles of Microwave Combination
Heating". Comprehensive Reviews in Food Science and Food Safety. 12 (1): 24–
39. doi:10.1111/j.1541-4337.2012.00211.x. ISSN 1541-4337.

Thank You