Tʜᴇ Sᴘᴇᴇᴅ ᴏғ ʟɪɢʜᴛ

                    8 - 11

electromagnetic waves never speed up or slow down

if they do, the wave would die out

speed of light - c, 2,999,792,458 m/s

before 1600s, Johannes Kepler, Rene Descarte believe

light to be transmitted instaneously

Galileo Galilei first to question this viewpoint

proposed experiment where 2 participants uncovered lanterns

determine speed of light with distance

limited by timekeeping methods and human reaction speed

estimate light was at least 10x faster than speed

in 1676, Danish astronomer Ole Romer noticed eclipses of 

Io happen later when Earth is father away and vice versa

calculated speed of light to be 220,000,000 m/s

around 1850, French physicist Hippolyte Fizeau used 

cogwheel and mirror 8km apart

obtain value of 313,000,000m/s for c

in 1862, fellow French Leon Foucault replace cogwheel

with rotating mirror, value of 298,000,000 m/s

in 1865 paper, James Maxwell use system of equations to

determine value of 300,000,000 m/s

concluded light was an electromagnetic wave

light and magnetism affections of the same substance, follows

electromagnetic laws

Albert Michelson, 1879, measurement 299,774,000 m/s

speed of light one of most well established value in physics,

we define length of meter in terms of it

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         Electromagnetic

             Spectrum

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continuum of electromagnetic waves, arranged by either

frequency or wavelength called electromagnetic spectrum

label for each category does not indicate fundamental differences

manifestation of the same electromagnetic wave phenomenon,

differing from one another in frequency of oscillation

directly related to amount of energy they are capable of 

depositing in matter

radio - 30 cm or longer, up to 1 km, tv, radar, satellites, walkie-talkie

microwaves - 1 mm - 30 cm, aircraft navigation, radar, research

infrared - 700 nm - 1 mm, cause objects to get hotter when

absorbed by increasing kinetic energy of atoms, meteorology,

night vision, communication, astronomy

visible - 400 nm - 700 nm, peak of human eye sensitivity around

560 nm, yellow green

ultraviolet - 400 nm - 10 nm, sun is significant source, most

absorbed by atmosphere, harmful to humans in large doses,

practical uses in sterilization of medical instruments

x-ray - 10x-4 nm - 10 nm, examination of bones, teeth, organs,

harmful to living tissue

gamma rays - short wavelength, highly penetrating, 10x-14 m -

10x-10 m, extremely hazardous to living tissue, causes irreversible

damage, but can kill cancer cells

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           Antennas and 

           Radio Waves

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antennas used to transmit and receive ems waves

when electrons in antenna are moved back and fourth, ems

wave is produced with matching frequency

in 1887, German physicist Heinrich Hertz generated first

radio waves in lab

exhibit similar properties to light waves, able to focus

and redirect them using reflective surfaces

unit of frequency hertz is named after him

death in 1894, Hertz believed radio waves served no practical

use beyond verifying Maxwell's equations

in mid 1890s, Italian engineer Gulielmo Marconi harness

radio waves for purposes of wireless communication

first public demonstration of radio transmitter and receiver in

July 1896