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

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

Radio wave

Less than 1 GHz


Microwave

Microwave

1 GHz to 3  1011 Hz

30 cm to 1 mm


Space communication

Space communication

Atmosphere is transparent from

less than 1 cm to 30 m

Also suitable for radio astronomy


The 21 cm hi radiation

The 21 cm HI radiation


Star and gas distribution

Star and Gas Distribution


Radio interferometric arrays

Radio Interferometric Arrays

32 MHz bands with 128 separate channels


Hi in galaxies

HI in Galaxies

DDO 210 Source: Begum and Chengalur

Dwarf Irregular Galaxy


Cosmic microwave background radiation

Cosmic Microwave Background Radiation

T=2.73 K

CMBR


Blackbody radiation

Blackbody Radiation


Molecular rotations

Molecular Rotations

Water 2.45 GHz used in microwave ovens

Excites Rotations of water molecules

50 GHz to 10 THz T-rays


Infrared

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

Visible Light

3.84  1014 Hz to 7.69  1014 Hz

Mainly atomic transitions – outer levels

Hot bodies ~5000K


Ultraviolet

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

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

Centaurus Cluster

Credit: J. Sanders, A. Fabian,


Gamma rays

Gamma Rays

Frequency greater than 5  1019 Hz

Produced in nuclear transitions

Electron-positron annihilation

Easy to detect – ionizes gas


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