This podcast provides a comprehensive look at microwave ovens, drawing on information concerning their functionality, safety regulations, cooking capabilities, and historical development.

The core of a microwave oven's operation lies in its use of microwaves, a form of electromagnetic radiation that is non-ionizing, meaning it doesn't carry the same risks as X-rays. Inside the oven, a device called a magnetron produces these 2.45 GHz microwaves. These waves have three key characteristics: they are reflected by metal, pass through materials like glass, paper, and plastic, and are absorbed by foods. When absorbed, microwaves cause water molecules in food to vibrate, generating friction and producing heat that cooks the food. Foods with higher water content cook more quickly because microwaves penetrate moisture efficiently. The energy is converted to heat upon absorption, so food does not become "radioactive" or "contaminated". The internal electromagnetic field creates an oscillating pattern of high and low intensity spots, known as standing waves, which is a primary reason for uneven heating in food. Different ingredients within a meal also absorb energy at varying rates based on their water content, contributing to this unevenness. Rotating the food, often on a glass plate or turntable, helps distribute the heat more evenly.

Safety is a significant focus, with the Food and Drug Administration (FDA) regulating the manufacture of microwave ovens since 1971. Manufacturers must certify that their products meet strict radiation safety standards. A federal standard limits microwave radiation leakage to 5 milliwatts (mW) per square centimeter at approximately 2 inches from the oven surface, a level far below that known to harm people. Ovens are equipped with two independent interlock systems that stop microwave production when the door is opened or the latch is released, along with a monitoring system in case of failure. While high levels of microwaves can heat body tissues and potentially cause skin burns or cataracts, most injuries related to microwave ovens are heat-related burns from hot containers, overheated foods, or super-heated water. Super-heated water, which appears not to be boiling even when past its boiling temperature, can violently erupt if disturbed. Modern pacemakers are generally shielded against electrical interference, resolving past concerns about microwave oven radiation.

The microwave oven's origins trace back to an accidental discovery in 1946 by Dr. Percy Spencer while working with a magnetron. This led to the first commercial model, the "Radarange," in 1947, and later to the more compact and affordable countertop domestic ovens that became widely adopted in American homes by the 1970s.