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Manisha Chowdhury asked:
Why is it called a microwave oven?
Who invented it?
What is the principle of its working?
A microwave oven is used to cook (or heat) food with the help of microwaves produced by magnetron – the device producing microwaves in the oven. Microwave ovens are so quick and efficient because they channel heat energy directly to the molecules (tiny particles) inside food.
Who invented Microwave Oven?
Percy Spencer is generally credited with inventing the modern microwave oven after World War II from radar technology developed during the war. Named the “Radarange”, it was first sold in 1946. Raytheon later licensed its patents for a home-use microwave oven that was first introduced by Tappan in 1955, but these units were still too large and expensive for general home use. The countertop microwave oven was first introduced in 1967 by the Amana Corporation, and their use has spread into commercial and residential kitchens around the world.
Working of microwave oven
A microwave oven, commonly referred to as a microwave, is a kitchen appliance that heats and cooks food by exposing it to electromagnetic radiation in the microwave spectrum. This induces polar molecules in the food to rotate and produce thermal energy in a process known as dielectric heating. Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer25–38 mm (1–1.5 inches) of a homogenous (high water content) food item; food is more evenly heated throughout (except in heterogeneous, dense objects) than generally occurs in other cooking techniques.
A microwave oven heats food by passing microwave radiation through it. Microwaves are a form of non-ionizing electromagnetic radiation with a frequency higher than ordinary radio waves but lower than infrared light. Microwave ovens use frequencies in one of the ISM (industrial, scientific, medical) bands, which are reserved for this use, so they don’t interfere with other vital radio services. Consumer ovens usually use 2.45 gigahertz (GHz)—a wavelength of 12.2 centimetres (4.80 in)—while large industrial/commercial ovens often use 915 megahertz (MHz)—32.8 centimetres (12.9 in). Water, fat, and other substances in the food absorb energy from the microwaves in a process called dielectric heating. Many molecules (such as those of water) are electric dipoles, meaning that they have a partial positive charge at one end and a partial negative charge at the other, and therefore rotate as they try to align themselves with the alternating electric field of the microwaves. Rotating molecules hit other molecules and put them into motion, thus dispersing energy. This energy, when dispersed as molecular vibration in solids and liquids (i.e. as both potential energy and kinetic energy of atoms), is heat.
For more details refer to :
An electron is moving with velocity v in an atom with orbital radius R. Derive the expression for magnetic moment of the electron.
Posted by Sankhadip Das
Find below a conversation between Master Deepak, PUC student and Mr. Mathew Abraham, Physics teacher.
Deepak asked: “nuclear fusion or fission in which of these energy released is more and why?”
Nuclear fusion requires very high temperature to start. It is difficult to maintain such a huge temperature (of the order of million degrees).
Research is going on to construct nuclear fusion reactor
Plutonium decays with a half-life of 24000 years.If plutonium is stored for 72000 years.What fraction of it remains?
I read in a biographic book about Albert Einstein that the energy produced from burning materials is much less than the energy stored in them (the authored suggested the book itself as an example – he wrote that it can power a ship for about 100 years).
I would like to know how much of the energy of a material is used in nuclear fission and fusion.
Energy obtained by burning a substance is meagre compared to the energy contained in it. According to Einstein’s mass energy relation (E=mc2), the energy released by converting 1 gram of any substance completely into energy = 0.001 (mass) x 300,000,000 x 3,00,000,000 (square of velocity of light).
But, in nuclear reactions, the entire mass is not converted into energy. The tremendous energy liberated during a nuclear explosion is the result of a small portion of the mass of nucleus undergoing the reaction getting converted into energy.
For example, when a uranium 235 atom undergoes nuclear fission the enrgy liberated is 200 MeV = 200 x 1.6 x 10 -19 J
In 235 g of U-235 there are 6 x 1023 atoms.
So if that much of U-235 atoms undergo fission, the energy liberated will be about 1,00,00,000 J.
Hope that you might have had an idea of it.
When it is not contested scientifically that change is a continuous phenomenon,how is that Higgs boson, if found,can be considered as the ultimate building block of matter.
Sure, it may prove a mathematically arrived conclusion… yet the contradiction remains.
An ever changing, at the same time, ever stable (because it is the ultimate one) is the contradiction.
One may find changing or divisible particle only…
(Posted by K.C. Muralidhar)
Please post your thoughts and reactions as comments to this post
Is it possible to stop a nuclear reaction,after starting it ( I’m not only talking about reactor, but in nuclear bombs too ). If it’s possible then which laws will fail or If It is impossible then Why? …………. have any country have prepared about It? (Asks George)