The Electromagnetic Spectrum

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The Electromagnetic Spectrum
PHYSICS 1

• Somnath Bharadwaj and Pratik Khastgir,
  Department of Physics and Meteorology, IIT
  Kharagpur, 721 302 India
• http//www.cts.iitkgp.ernet.in/phy1/

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Radio wave
Less than 1 GHz
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Microwave
1 GHz to 3 ? 1011 Hz
30 cm to 1 mm
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Space communication
Atmosphere is transparent from less than 1 cm to
30 m
Also suitable for radio astronomy
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The 21 cm HI radiation
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Star and Gas Distribution
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Radio Interferometric Arrays
32 MHz bands with 128 separate channels
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HI in Galaxies
DDO 210 Source
Begum and Chengalur
Dwarf Irregular Galaxy
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Cosmic Microwave Background Radiation
T2.73 K
CMBR
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Blackbody Radiation
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Molecular Rotations
Water 2.45 GHz used in microwave ovens Excites
Rotations of water molecules
50 GHz to 10 THz T-rays
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Infrared
3 ? 1011 Hz to 4 ? 1014 Hz
Near IR 760 - 3000
nm Intermediate IR 3000 - 6000 nm Far IR
6000 - 15000 nm Extreme IR
15000nm 1 mm
Human body peaks at 10000 nm
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Visible Light
3.84 ? 1014 Hz to 7.69 ? 1014 Hz
Mainly atomic transitions outer levels Hot
bodies 5000K
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Ultraviolet
8 ? 1014 Hz to 3 ? 1016 Hz Enough energy to
ionize atoms in upper atmosphere Is harmful
absorbed by O3 in upper atmosphere Produced in
energetic atomic transitions
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X-ray
2.4 ? 1016 Hz to 5 ? 1019 Hz Energetic electrons
incident on a metal Hot astrophysical sources
Black Holes Inner shell transitions in atoms
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Centaurus Cluster
Credit J. Sanders, A. Fabian,
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Gamma Rays
Frequency greater than 5 ? 1019 Hz Produced in
nuclear transitions Electron-positron
annihilation Easy to detect ionizes gas