How do microwaves heat things?

Answer 1

Microwaves are electromagnetic radiation and part of the Electromagnetic Spectrum, along with radio waves, infrared, light, ultraviolet, x-rays, and gamma rays. Microwaves do not have enough energy to remove electrons from the orbits of atoms, putting it in the class of non-ionizing radiation. Electromagnetic radiation is energy in transfer by electromagnetic waves. These waves move at the speed of light. Microwaves have a range of frequencies of 0.03 to 300 GHz, placing it between Radio-frequency and Infrared radiation in the Electromagnetic Spectrum. Hertz (Hz) is a measure of frequency, the number of times per second that the waves oscillate, in the electric and the magnetic directions. (Note: "GHz" means a billion hertz, or a billion of times per second ). Microwave ovens often use 0.9 or 2.5 GHz for their heating frequencies.

The way microwaves heat things, according to Professor Herman Cember in his book Introduction to Health Physics (Pergamon Press):

In its interaction with matter, microwave energy may either be reflected, as in case of metals, it may be transmitted with little energy loss to the transmitting medium, as in the case of glass, or it may be absorbed by irradiated matter, and thus raise the temperature of the absorber. This heating is attributed to two effects: the main mechanism is believed to be joule heating due to ionic currents induced by the electric fields that are set up within the absorbing medium by the radiation. The second mechanism is due to the interaction between polar molecules in the absorber and the applied high-frequency electric field. The alternating electric field causes these polar molecules to oscillate back and forth in an attempt to maintain the proper alignment in the electric field. These oscillations are resisted by other intermolecular forces, and work done by the alternating electric field in overcoming these resistive forces is converted into heat.

In other words, the EM waves oscillate at high frequency, and set up currents and move molecules. The moving molecules and current generate heat. It has nothing to do with excitation.

Water is a polar molecule and has good heat transfer, so it is a good microwave-able material. Many biological molecules are also polar. The microwaves penetrate most materials to a depth of 1-2 cm. The heat is then transferred by conduction to the whole of the material..

Answer 2

Microwave ovens are tuned so that the microwaves (part of the spectrum of electro-magnetic radiation) are absorbed by water (and certain other) molecules, which therefore heat up. Water occurs in virtually anything you might want to cook. Even dried maize has some residual water, hence the effectiveness of microwaves for making popcorn. The microwaves will typically penetrate a short distance (a few cm) before being fully absorbed, so food is not specifically heated on the outside but throughout (so long as the food is not too thick). Conduction will continue the cooking process to deeper levels, but takes longer. The amount of energy needed to cook food in a microwave is proportional to its weight, so heating up two take-away meals will take twice as long as heating one, whereas in a conventional oven two will heat up in the same time as one. Containers such as ceramic, plastic and glass do not contain water so do not heat up, except by conduction from what they contain. Metal reflects and channels microwaves, which can be dangerous and damaging unless designed in (eg some microwave ovens have metal shelves). Some ceramics have glazes that contain metal, and should not be used in a microwave oven.

Answer 3

Microwaves don't have a heating effect as thought of.
They don't have any hetaing element ,instead they us the concept of elctronic collisions inside the atoms of heated object due high energy transferred to them by the Microwave Radiations.

Answer 4

In a microwave, microwave radiation causes electrons of food items to agitate generating heat which cooks them which depends on exposure time which is different for each cooking.

Answer 5

as it has got very hot temperature in it