Microwaves

The microwave oven was a by-product of another technology. It was during a radar-related research project around 1946 that Dr. Percy Spencer, a self- taught engineer with the Raytheon Corporation, noticed something very unusual.

He was testing a new vacuum tube called a magnetron, when he discovered that the candy bar in his pocket had melted.

This intrigued Dr. Spencer, so he tried another experiment. This time he placed some popcorn kernels near the tube and, perhaps standing a little farther away, he watched with an inventive sparkle in his eye as the popcorn sputtered, cracked and popped all over his lab.

The next morning, Scientist Spencer decided to put the magnetron tube near an egg. Spencer was joined by a curious colleague, and they both watched as the egg began to tremor and quake.

Dr. Spencer fashioned a metal box with an opening into which he fed microwave power. The energy entering the box was unable to escape, thereby creating a higher density electromagnetic field. When food was placed in the box and microwave energy fed in, the temperature of the food rose very rapidly. Dr. Spencer had invented what was to revolutionize cooking, and form the basis of a multimillion dollar industry, the microwave oven.

Nearly 6 Feet Tall, Weighing 750 Pounds and costing about $5000 each

What are Microwaves ？ Microwaves are electromagnetic waves; consists of both electric and magnetic fields perpendicular to each other and propagates at the speed of light.

Magnetron tube changes electricity to microwave energy. The energy is reflected, transmitted, or absorbed.

Reflected Microwaves reflect off the walls of the oven. A stirrer fan helps reflect microwaves evenly for cooking.

Transmitted Microwaves pass through paper, glass, and plastic. Microwaves transmit food trough these materials.

Microwaves are short radio waves. They cause the molecules in food to vibrate.

Vibration Friction. Heat. Cooks the food.

Cooking Power Amount of energy oven uses to generate microwaves.

Cooking with Microwaves represents water molecule; represents molecules of food. Magnetron produces microwaves which pull the water molecules back and forth at the rate of about 2.5 billion times per second. This rapid back-and-forth motion between the water molecules creates friction, and hence heat. And then the heat is transferred to the molecules of food nearby.

Reflected by metal. Pass through glass, paper, plastic, and wax. Absorbed by water, fat and sugar molecules in food. Attracted to salt; wait until after cooking to salt the surface food.

What is arcing? Arcing is an electrical spark inside the microwave oven. It looks like lightning! It occurs when microwaves connect between two points of metal. It can cause a fire if flammable materials are inside the MW. It can damage the microwave oven.

CD in Microwave RF energy bounces off CD, makes neat sparks * This could cause damage to microwave

Lit Matchstick in Microwave Plasma of the fire rapidly absorbs the large amount of RF energy * This may damage your microwave

Tinfoil in Microwave This is why your mom told you to never put tinfoil in the microwave! This kicks out a tremendous amount of heat and noise. Will burn through glass

when-you-put-metal-in-a-microwave when-you-put-metal-in-a-microwave

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Normal Microwave Use RF energy excites water molecules Water molecules rotate on poles, friction with neighbor molecules Friction forces molecules to retain energy, otherwise it would just radiate energy away Hot Spots – causes uneven cooking