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Name: Mario
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Question:
Do all frequencies in the electromagnetic spectrum transmit heat, or is it just infrared light that heats the things it touches?



Replies:
Mario,

The electromagnetic spectrum is associated with waves that move at speed of light and have wavelengths that can be the very short gamma rays all the way through to the very long waves (longer than radio waves). Frequency and wavelength are related to each other by the following equation: frequency × wavelength = speed of light. All frequencies in the electromagnetic spectrum transmit energy at the speed of light.

The terms energy and heat are often used interchangeably and both have the same dimensions (mass × length^2 × time^-2) and use the units of joules, British Thermal Units, calories, electron volts, ergs, kilowatt hours, or similar measures). For an object to heat up, that is to gain energy that is measured as an increase in temperature, the energy source must resonate with the molecules of the material. A lot of material resonates with the frequency associated with the infrared wavelength.

Microwave ovens, however, operate at a frequency around 2450 MHz which is associated with a frequency slightly lower (that is, a longer wavelength) than what is commonly referred to as the infrared spectrum of wavelengths. The wavelength of a microwave oven resonates with the water molecule and thus makes the water molecule vibrate more quickly and the temperature rises. Hot materials will radiate energy in the infrared spectrum, yet they may be heated by wavelengths that are not in the infrared spectrum. There are other ways to heat matter that are not associated with resonant frequencies... can you think of one?

Leslie Kanat


The energy of a photon, E = h x f, where E is the energy, h = Planck's constant = 6.6 * 10^-34 and f = frequency of the electromagnetic photon. So all photons have energy -- that is the simple part. How a photon interacts with some matter it may encounter is more complicated. It can be reflected, absorbed, transmitted (i.e. the target is transparent). The photon can lower its frequency, becoming several photons of lower frequency, i.e. energy. The photon can interact in other ways (e.g. absorbed), and a lot of other processes can be initiated by this absorption, not just heating. To get directly to your question all frequencies of electromagnetic radiation, given the proper set up, can generate heat, not just infrared, but the various possible interactions may not be simple and direct.

Vince Calder



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