Microwave ovens heat food by using magnetrons to generate microwaves, a type of electromagnetic radiation. These waves specifically excite water molecules, causing them to vibrate and generate heat through friction. The oven's design, including the metal walls and turntable, ensures the waves are reflected and distributed throughout, although uneven heating can still occur due to variations in food density and moisture content. While some energy is absorbed by other molecules like fats and sugars, water's prevalence in most foods makes it the primary target. Contrary to some misconceptions, microwaving does not inherently make food radioactive or deplete its nutrients significantly, though overheating can destroy certain vitamins.
Magnetic fields, while seemingly magical, arise from the interplay of special relativity and electrostatics. A current-carrying wire, viewed from a stationary frame, generates a magnetic field that interacts with moving charges. However, from the perspective of a charge moving alongside the current, length contraction alters the perceived charge density in the wire, creating an electrostatic force that perfectly mimics the magnetic force observed in the stationary frame. Thus, magnetism isn't a fundamental force, but rather a relativistic manifestation of electric forces. This perspective simplifies understanding complex electromagnetic phenomena and highlights the deep connection between electricity, magnetism, and special relativity.
HN commenters largely praised the article for its clear explanation of magnetism, with several noting its accessibility even to those without a physics background. Some appreciated the historical context provided, including Maxwell's contributions. A few users pointed out minor technical inaccuracies or suggested further explorations, such as delving into special relativity's connection to magnetism or the behavior of magnetic monopoles. One commenter highlighted the unusual nature of magnetic fields within superconductors. Another offered an alternative visualization for magnetic field lines. Overall, the discussion was positive and focused on the educational value of the original article.
Summary of Comments ( 26 )
https://news.ycombinator.com/item?id=42961606
Hacker News users discuss the linked article about microwave ovens, focusing on the physics of how they work. Several commenters debate the specifics of how water molecules absorb microwave energy, with some emphasizing the importance of dipole rotation and others highlighting the role of hydrogen bonding. The potential dangers of uneven heating and "superheating" water are also mentioned, along with the impact of container material on heating efficiency. Some users share personal experiences and anecdotal observations regarding microwaving different substances. The overall tone is one of scientific curiosity and practical application of physics principles. A recurring theme is clarifying misconceptions about microwave ovens and explaining the underlying science in an accessible way. One commenter also questions the article's claim that metal in a microwave can cause damage, suggesting it's more nuanced.
The Hacker News post titled "Science of Microwave Ovens (2016)" linking to an article on genuineideas.com has several comments discussing various aspects of microwave ovens, their functionality, and their impact on food.
One commenter points out the difference between heating food in a microwave oven versus a conventional oven. They explain that microwaves primarily heat water molecules, leading to uneven heating and the "rubbery" texture often experienced with microwaved food. They contrast this with conventional ovens, which heat the food from the outside in, resulting in a more desirable texture and browning. This commenter also highlights the inefficiency of microwaves for cooking certain foods, like pizza, due to their reliance on water content for heating.
Another commenter focuses on the safety of microwave ovens, specifically addressing the misconception that they leak harmful radiation. They explain that modern microwave ovens are designed with shielding to prevent leaks and that the levels of radiation that might escape are negligible and pose no health risk. They further elaborate on how the door's design and safety interlocks work to ensure that the magnetron, the component generating microwaves, shuts off immediately when the door is opened.
The discussion also delves into the science behind microwave heating, with one commenter explaining the interaction between microwaves and water molecules. They describe how the electromagnetic waves cause water molecules to rotate, generating friction and thus heat. This comment also touches on the penetration depth of microwaves, explaining why larger or denser items take longer to heat as the microwaves cannot penetrate as deeply.
Further comments discuss specific uses of microwaves, such as melting chocolate, and offer practical tips like using a wooden skewer to prevent superheating in water. Some commenters also mention alternative heating methods, like induction cooking, and compare their efficiency and effectiveness to microwave ovens. One commenter briefly mentions the use of microwaves in industrial settings, illustrating their versatility beyond household applications.
Finally, there's a short thread discussing the history of microwave ovens, mentioning Percy Spencer's accidental discovery and the initial commercial applications of the technology. This thread also touches on the evolution of microwave oven design and features over time.