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 108 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…