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Principle of Working of Microwave Oven

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-spencerPercy 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

microwave ovenA 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.

Magnetron2A 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 :


FTL – Faster than light

Charan asked: In a recent research,it was found experimentally that nutreinos are faster than light.In that case,Einstein’s Relativistic mechanics don’t work.What tpe of mechanics are applied in that case?


There was a news about  faster than light by neutrinos recently by the scientists of CERN which they corrected later explaining that the news wa a result of mistake in calculation caused by the error in time interval reporting.

The scientists (and others too) are not yet ready to accept a result of faster than light travel by a material particle. So, if such an observation is reported, the scientific community is to be prepared with sufficient theoretical background to explain contrary to the Theory of Relativity.

What is Quantum Teleportation?

Quantum teleportation is a way of transferring a quantum state from one place to another without actually sending a particle in that state through space. (Source – Physicsworld.com)

Anton Zeilinger (right) of the University of Vienna has extended this distance to 143 km by teleporting quantum states across the stretch of sea separating two of the Canary Islands. The team claims that its triumph takes the prospect of quantum teleportation to and from satellites one step closer.

Zeilinger and co-workers teleported quantum states from La Palma to Tenerife, and to pull it off they had to develop several new technologies including a new source of entangled photon pairs and “ultra-low-noise” single-photon detectors. Timing also proved to be a challenge, because the 10 ns uncertainty in GPS timing signals was not good enough to achieve the teleportation. Instead, the team had to develop a new “entanglement-assisted clock synchronization” technique that relies on the detection of the entangled photons

What’s the use of Quantum Teleportation?


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Mystery Spot and Physics

Mystery spot is a tourist attraction located near Santa Cruz , California. It is a place where the laws of physics and gravity do not apply.
The Mystery Spot is a gravity hill, a tilt indused visual illusion. In the tilted room of the mystery spot , misperceptions of the height and orientation of objects occur. Explain.

(Asked by G Saranya)


The question on gravity hills (also called magnetic hills) is already answered. Please refer to http://askphysics.com/gravitation/magnetic-hills-gravity-hills/

Apparent weight in an elevator

You are standing on a bathroom scale in an elevator the is moving upward at constant speed, when suddenly the cable breaks. from just before to just after the cable breaks, the reading on the scale will be?

When the elevator is moving up with constant speed, the bathroom scale (weighing scale) shows the correct weight, because the mechanics involved will be the same if the frame is at rest or moving with a constant velocity.
When the cable breaks, it is a case of freely falling body and the scale reads zero.

Why a sound is produced when a fluorescent tube breaks?

Why does a big  sound come when tube-light breaks?

(Question was posted by Vishwesh)

Answer: Every sound is produced by some vibrating bodies. In this case it is air surrounding the tube which vibrates.

Broken Tube LightInside the tube-light there is partial vacuum. When it breaks, the air surrounding the tube suddenly rushes into the vacuum and starts vibrating and thus produces the sound.

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