All about temperature and heating, energy, magnetron, microwave ovens

Temperature is a measure of the average kinetic energy of the particles in a substance: the faster the particles move, the higher the temperature. It is distinct from heat, which is the energy transferred between objects because of a temperature difference. Several scales are used to express temperature. The Celsius scale sets zero at the freezing point of water and one hundred at its boiling point under standard pressure, while the Kelvin scale starts at absolute zero, the lowest possible temperature, at which particle motion is at its minimum.

Absolute zero corresponds to about minus 273 degrees Celsius. Because the Kelvin and Celsius scales use the same size of degree, converting between them simply requires adding or subtracting that offset. The Kelvin scale is preferred in science because thermal energy is proportional to absolute temperature, making physical relationships simpler to express.

Heat moves from warmer to cooler regions by three mechanisms. Conduction transfers energy through direct contact as fast-moving particles collide with slower ones; convection carries heat through the bulk movement of a heated fluid; and radiation transmits energy as electromagnetic waves that need no medium, which is how the Sun warms the Earth. A microwave oven heats food differently, using microwave radiation to make water molecules rotate rapidly, and the resulting molecular motion warms the food from within rather than from an external hot surface.

Frequently asked questions

What is the difference between heat and temperature?: Temperature measures the average kinetic energy of particles, while heat is the energy that flows between objects because of a temperature difference.
What is absolute zero?: Absolute zero is the lowest possible temperature, about minus 273 degrees Celsius or zero kelvin, where particle motion reaches its minimum possible value.
How does a microwave oven heat food?: It emits microwaves that cause water molecules in the food to rotate rapidly. The friction from this motion generates heat throughout the food rather than only at the surface.

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Thermal physics

related subjects: Thermo dynamics, Microwave ovens, Thermal Physics

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