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/. Radio wave. Less than 1 GHz. Microwave. 1 GHz to 3  10 11 Hz. 30 cm to 1 mm.

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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/


Radio wave

Less than 1 GHz


Microwave

1 GHz to 3  1011 Hz

30 cm to 1 mm


Space communication

Atmosphere is transparent from

less than 1 cm to 30 m

Also suitable for radio astronomy


The 21 cm HI radiation


Star and Gas Distribution


Radio Interferometric Arrays

32 MHz bands with 128 separate channels


HI in Galaxies

DDO 210 Source: Begum and Chengalur

Dwarf Irregular Galaxy


Cosmic Microwave Background Radiation

T=2.73 K

CMBR


Blackbody Radiation


Molecular Rotations

Water 2.45 GHz used in microwave ovens

Excites Rotations of water molecules

50 GHz to 10 THz T-rays


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


Visible Light

3.84  1014 Hz to 7.69  1014 Hz

Mainly atomic transitions – outer levels

Hot bodies ~5000K


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


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


Centaurus Cluster

Credit: J. Sanders, A. Fabian,


Gamma Rays

Frequency greater than 5  1019 Hz

Produced in nuclear transitions

Electron-positron annihilation

Easy to detect – ionizes gas


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