Radiasi éléktromagnétik

Gelombang elektromagnetik (EM) nyaeta kabeh gelombang anu dihasilkeun tina interaksi antara medan listrik jeung medan magnet. Gelombang EM ngawengku gelombang-gelombang ti mimiti nu panjangna rebuan kilometer tepi sapondok ukuran atom. Umumnya disebutkeun yen gelombang EM anu panjangna di luar wates-wate kasebut henteu lumrah, sanajan anggapan ieu henteu sakabehna bener. Batas gelombang pondok kamungkinan ngarupakeun gelombang Planck, jeung wates panjang gelombang pang panjangna saukuran jeung jagat (tingali kosmologi fisika), sanajan dina dasarna spektrum teh taya hingga.

^[rujukan?]Legend
γ = Gamma rays
HX = Hard X-rays
SX = Soft X-Rays
EUV = Extreme ultraviolet
NUV = Near ultraviolet
Visible light
NIR = Near infrared
MIR = Mid infrared
FIR = Far infrared

Radio waves
EHF = Extremely high frequency (Microwaves)
SHF = Super high frequency (Microwaves)
UHF = Ultra high frequency
VHF = Very high frequency
HF = High frequency
MF = Medium frequency
LF = Low frequency
VLF = Very low frequency
VF = Voice frequency
ELF = Extremely low frequency

Enerji elektromagnetik dina sahiji panjang gelombang λ (dina ruang hampa) miboga sahiji frekuensi f jeung enerji foton E. Jadi, spektrum elektromagnetik bisa dinyatakeun dina tilu kuantitas ieu. Katilu kuantitas ieuc dihubungkeun ku rumus:

laju gelombang (c) = frekuensi x panjang gelombang

atawa

$\lambda ={\frac {c}{f}}\,\!$

jeung

$E=hf\,\!$

atawa

$E={\frac {hc}{\lambda }}\,\!$

dimana:

• c nyaeta laju cahaya, 299,792,458 m/s (pasti).
• h nyaeta konstanta Planck, Peta ''parse'' gagal (fungsi teu kanyahoan): {\displaystyle (h \kira-kira 6.626069 \cdot 10^{-34} \ \mbox{J} \cdot \mbox{s} \approx 4.13567 \ \mathrm{\mu} \mbox{eV}/\mbox{GHz})} .

Jadi, gelombang elektromagnet frekuensi luhur miboga panjang gelombang nu pondok jeun enerji anu gede; gelombang elektromagnet frekuensi handap miboga panjang gelombang anu panjang sarta enerji anu saeutik.

Mangsa gelombang cahaya (jeung gelombang elektromagnetik lianna) asup kana sahiji mediyeum, panjang gelombangna ngurangan. Panjang gelombang radiasi elektromagnetik, teu paduli mediyeum naon anu diliwatanna, biasana dirumuskeun dikaitkeun jeung panjang gelombang ruang hampa, sanajan hal ieu teu salawasna dinaytakeun sacara jelas.

Spectra of objects

Electromagnetic Spectrum Image.

Nearly all known objects in the universe emit, reflect or transmit some light. (One exception, however, may be dark matter, which, along with Dark energy may make up 96% of the universe's total mass.) The distribution of this light along the electromagnetic spectrum (called the spectrum of the object) is determined by the object's composition. Several types of spectra can be distinguished depending upon the nature of the radiation coming from an object:

• If the spectrum is composed primarily of thermal radiation emitted by the object itself, an emission spectrum occurs.
  • Some bodies emit light more or less according to the blackbody spectrum.
• If the spectrum is composed of background light, parts of which the object transmits and parts of which it absorbs, an absorption spectrum occurs.

Electromagnetic spectroscopy is the branch of physics that deals with the characterization of matter by its spectra.

Gambar:Incandescent lamp spectra.png

Spectrum of incandescent lamp, in IR range, with b/g noise in yellow

A Halogen incandescent lamp, has a light spectra as shown in the accompanying figure. The figure shows just the infrared end of the whole spectra, which is limited by the resolution of the spectrum analyzer from 600 nm to 1500 nm, in the optical window, typical to fiber optic communication systems.

External links

• U.S. Frequency Allocation Chart — Covering the range 3 kHz to 300 GHz (from Department of Commerce)
• Canadian Table of Frequency Allocations (from Industry Canada)
• UK frequency allocation table (from Ofcom, which inherited the Radiocommunications Agency's duties, pdf format)
• The Science of Spectroscopy - supported by NASA, includes OpenSpectrum, a Wiki-based learning tool for spectroscopy that anyone can edit

See also

• W_band
• V_band