Study Guide: Microwaves
What is Microwave Radiation?
Microwaves are a form of electromagnetic radiation; that is, they are waves of electromagnetic energy moving through space.
Electromagnetic radiation spans a broad spectrum from very long radio waves to very short gamma rays. The human eye can only detect a small portion of this spectrum called visible light. A radio detects a different portion of the spectrum, and an X-ray machine uses yet another portion. Visible light, microwaves, and radio frequency (RF) radiation are forms of non-ionizing radiation. Non-ionizing radiation does not have enough energy to knock electrons out of atoms.
X-Rays
X-rays are a form of ionizing radiation. Exposure to ionizing radiation can alter atoms and molecules and cause damage to cells in organic matter. Microwaves are used to detect speeding cars and to send telephone and television communications. Industry uses microwaves to dry and cure plywood, to cure rubber and resins, to raise bread and doughnuts, and to cook potato chips. But the most common use of microwave energy is in microwave ovens. Microwaves have four characteristics that allow them to be used in cooking:
- Reflected by metal
- Pass through glass, paper, plastic, and similar materials
- Absorbed by foods
- Cause water molecules to vibrate
How Microwave Ovens Work
Microwaves are produced inside the oven by an electron tube called a magnetron. The microwaves are reflected within the metal interior of the oven where they are absorbed by food.
Microwaves cause water molecules in food to vibrate, producing heat that cooks the food. That’s why foods high in water content, such fresh vegetables, can be cooked more quickly than lower water content foods.
The microwave energy is changed to heat as it is absorbed by food, and does not make food “radioactive” or “contaminated.” Although heat is produced directly in the food, microwave ovens do not cook food from the “inside out.” When thick foods are cooked, the outer layers are heated and cooked primarily by microwaves while the inside is cooked mainly by the conduction of heat from the hot outer layers.
Microwave cooking can be more energy efficient than conventional cooking because foods cook faster and the energy heats only the food, not the whole oven compartment. Microwave cooking does not reduce the nutritional value of foods any more than conventional cooking. In fact, foods cooked in a microwave oven may keep more of their vitamins and minerals, because microwave ovens can cook more quickly and without adding water.
Glass, paper, ceramic, or plastic containers are used in microwave cooking because microwaves pass through these materials. Although such containers are not directly heated by microwaves, they can become hot by heat conduction from the heated food.
Some plastic containers should not be used in a microwave oven because they can be melted by heat transferred food.
Generally, metal pans or aluminum foil should not be used in a microwave oven, as the microwaves are reflected off these materials causing the food to cook unevenly and possibly damaging the oven.
Super-Heated Water
The US Food and Drug Administration (FDA) has received reports of serious skin burns or scalding injuries around people’s hands and faces as a result of hot water erupting out of a cup after it had been overheated in a microwave oven.
Super-heated water (water heated past its boiling temperature) does not appear to be boiling. It can occur when pure water is heated in a clean container. If super-heating occurs, a slight disturbance or movement such as picking up the cup, or pouring in a spoonfull of instant coffee, may result in a violent eruption with the boiling water exploding out of the cup. Adding substances such as instant coffee or sugar before heating greatly reduces this risk.
Vocabulary
- Microwaves
- Electromagnetic radiation
- Spectrum
- Magnetron
- Visible light
- Radioactive
- Super-heated water
- Scalding injuries
- Radio frequency (RF) radiation
- Non-ionizing radiation
- FDA