🚀 go-pugleaf

WHAT DO MICROWAVE COOKING AND LIGHTNING HAVE IN COMMON? BOTH ARE WIDELY KNOWN
AND POORLY UNDERSTOOD. LET'S SHARE WHAT WE KNOW ABOUT THE PHYSICS INVOLVED.
This note (with references) is being posted in that spirit. It is a reply to
a thoughtful message sent to me several days ago by X from Philadelphia.

Dear X;
    I read your reply and I agree with your observations. In new experiments
with liquids I am comparing absorbed heats rather than temperatures. Specific
heat of the beaker is taken under account. It is hard to keep conditions
identical; I try the best I can. I am studying the effect of salt on the heat
deposited in water. The book on microwave cooking, which was suggested to me
several days ago, states that salty water (5% NaCl) will be heated ten times
more than pure water; my salt solution took less heat than pure water. I must
look at this again more carefully.

The book I am referring to is "Microwave Cooking and Processing, Engineering
Fundamentals for the Food Scientist", by Charles R. Buffler. It was published
in 1993 by Van Nostrand Reihold; good to have in a school library. I also
learned about two magazines devoted to the subject: Microwave World and
Journal of Microwave Power. According to a recent article, microwave ovens are
used in 90% of US households (they started to be popular in 1975, ten years
later they were used in 50% households.)

The problem of "what happens to the energy which is not absorbed in food" is
tricky. Only a very small part of it is absorbed in the cooking cavity. Most
of it probably goes back to the magnetron and its wave guide to be absorbed
there. Can the system be compared to an electric battery which heats resistors
according to the "impedence matching" rule? I do not know. A typical oven
takes 1500 W of electric energy and delivers heat at the rate of 700 W to a
"full load" of food. This means that 800 W is normally dissipated in the
generator which is cooled by a fan. Heating a very small sample (or an empty
oven) would nearly double that amount and increase the source temperature. An
electric battery is "smarter"; it slows down chemical activities when the
outside resistance is increased. Can ovens be designed to take only as much
energy as needed without the unnecessary wastes? Future inventors would be
challenged by such questions.

Your observations are engaging, you should share them on the network.
There is a lot of intersting physics in microwave cooking.

         Ludwik Kowalski   kowalski@apollo.montclair.edu