Electromagnetic Radiation

LIGHT

Electric fields Exist around electric charges Moving electric fields create magnetic fields Magnetic field perpendicular to electric field Electric field causes current and therefore produces magnetic field

Alternating current Produces sine wave as electrons oscillate (AC current) (DC voltage does not produce a wave) Changing electric field creates changing magnetic field Changing magnetic field creates changing electric field Energy transmitted through space as electromagnetic waves (electromagnetic energy)

Electromagnetic waves Travel through space at 3 * 10 8 m/s All wavelengths and all frequencies travel at same speed through same medium. C = f

Electromagnetic spectrum Based on wavelengths Divided into bands based on wavelengths Longest  shortest: – Radio – Micro – Infrared – Visible – Ultraviolet – X-rays – Gamma rays

Spectroscopy Study of interactions of electromagnetic radiation (primarily visible light) with molecules Electromagnetic Radiation - not just visible light!!

Radio Waves Transmit radio and TV signals Not affected by sunlight, clouds, rain Used to detect composition of galaxies, stars

Microwaves Satellite communication, radar tracking (Doppler radar [radio detection and ranging]), heating food Penetrate haze, dust, clouds, so good for viewing earth from satellites

Infrared Perceived as heat Used in heaters, remote sensing, remote controls Fire, human body temps, land and water temps, galaxy emissions

Landsat Images used to view “invisible” features on earth, including cloud structure

Visible Light Sun radiates ALL frequencies, but in diff. amounts Some absorbed, some reradiated (reflected) White light contains many colors; all reflected equally Color used to enhance images of things we want to see. Ex.: clouds on Jupiter Crab Nebula (real and false) and Uranus (real and false)

Ultraviolet Causes sunburns/tans Used to purify water, food Most absorbed in upper atmosphere Insects can see in UV UV from sun, moon, different stars

X Rays Highly penetrating Used in airport security, checking welds for flaws, detecting fake gems, medical diagnostics, space research Shown: views of comet, binary star, supernova, sun

Gamma Rays Very penetrative. Kill bacteria, alter DNA, used in space exploration Gamma rays from moon, galaxy Crab nebula (gamma, then visible light)

Cosmic radiation Mostly protons, some He nuclei (  alpha particles), and a few electrons (  Beta particles) Commonly lumped together as muons May be used to detect hidden nuclear material