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Electromagnetic Spectrum, Energy Transfer, Heat
Name: Mario
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
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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Update: June 2012
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