Electromagnetcetera… Chapter 18

Electromagnetic Waves Constantly changing fields: –Electric field –Magnetic field

EMW’s Produced when electric charge vibrates or accelerates ***Do NOT need a medium to travel in. *Electromagnetic Radiation – transfer of energy by EMW through matter or space

Speed of EMW’s In a vacuum… ALL EMW’s travel same speed. c = 3.00 X 10 8 m/s -EMW’s vary in wavelength and Hz. -S = W X F

Wave or Particle? WAVE = -Thomas Young (P. 536) -Experiment showed bands of interference PARTICLE = -photoelectric effect -Einstein (photons – packets of energy)

Phillip Lenard – experimented/coined term…

Intensity Light (photons) travel outward from source in ALL directions. –Intensity decreases as light travels farther…

Electromagnetic Spectrum

Radio Waves Amplitude Modulation – amplitude is varied (AM stations) Frequency Modulation – frequency varied (FM stations) (Television) **Radio waves = longest waves

Microwaves –Cook food –Cell phones Radar –Cops –Baseball

Infrared Rays Used to discover sources of heat and heat differences –Marijuana (heat lamps) Heat source –Fast food

Visible Light Only light human eye can see.

Ultraviolet Rays Source of vitamin D Medicine, agriculture (greenhouses) UVA, UVB? Wear sunscreen?

X-Rays Can penetrate matter that light can’t. Medical, dental x-rays Airport, courthouses, etc.

Gamma Rays Shortest wavelengths Overexposure = death Treat cancer - radiation

Light Behavior Transparent Translucent Opaque

Reflection Regular –mirror Diffuse –rough surface

Refraction Light bends or curves

Polarization Polarized light vibrates in one plane –Vertical or horizontal Sunglasses Car visors

Scattering Light is redirected as it passes through a medium Why is the sky blue? Blue light scatters the most… filling the sky… to make it appear blue… but…