ᴠɪsɪʙʟᴇ ʟɪɢʜᴛ ᴀɴᴅ ᴄᴏʟᴏᴜʀ

 

                12 - 15

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     The Visible Spectrum

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colours we see depend on frequencies of light that

reaches our eyes

lowest is red, highest is violet

colour is not inherent property of ems waves, nor 

an object of within the object

colour is a physiological experience involving 

eyes and brain, differs from person to person

appears white -  light made up of all colours

late 1660s - Sir Issac Newton use prism to separate

sunlight into spectrum of colours, recombine them 

with second spectrum

sun emits range of ems waves, over 99% belonging 

to uv, visible, and infared

peak of colour intensity resides within visible spectrum

for humans

some animals sensative to waves not visible to humans

Bees - detect UV patterns towards pollination sites

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     Selective Absorption

          and Reflection

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we see sources of visible light because they emit ems

waves in visible spectrum 

we also see objects that aren't sources of light, because

they reflect light from other sources to our eyes

objects absorb light of certain frequencies and reflect

the rest

frequency of reflected light determines colour

incandescent bulbs - tend to emit low frequency waves,

objects appear more warm

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    Selective Transmission

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glass is colourless because it transmits all frequencies

of light equally well

materials can absorb some, transmit other frequencies

rubies - variety of corundum (naturally colourless),

gain colour due to chromium impurities 

sapphires - same as rubies, contain titanium and iron

possible to artificially produce materials transparent 

only to certain frequencies

cobalt blue glass - contains cobalt oxide

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            Blue Skies,

            Red Sunsets

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light not exactly reflected, but scattered off molecules

in atmosphere

molecular gases in atmosphers: N2, O2, Ar, CO2,

other gases in trace amounts

N2 and O2 molecules have resonant frequencies on

high end of visible spectrum, tend to scatter blue more

Rayleigh scattering (named after British physicist Lord

Rayleigh) 

violet light scattered more strongly, but our eyes more 

sensitive to blue

at sunset: light from sun travel further along atmosphere,

by the time sun reaches your eyes, higher frequencies

have scattered away, lower frequencies have not

Sunset in a Glass: clear glass, water, milk, bright

flashlight

blue when viewed at right angle to flashlight

red when viewed opposite the flashlight

similar to how light scatters off particles in atmosphere