OPTICAL PHENOMENAHow light can trick us
Naturally Occurring Phenomena
Apparent depth Flattened sun and sunsets Mirages Shimmering Rainbows
Apparent depth The depth that an object appears to be
due to the refraction of light in a transparent medium
Eg. Looking into water from above Light will refract away from the normal
travelling from water into air because air is faster
Our brains don’t acknowledge that the light is refracted, so we extend the refracted ray straight back, creating a virtual source of the light rays
Apparent DepthOBJECTS IN WATER APPEAR CLOSER TO THE SURFACE
PENCIL IN WATER APPEARS BENT
“Flattened” Sun When the sun nears the horizon, it
appears to be flattened during a sunset Light from the bottom of the sun is
refracted more than light from the top This is because the air lower in the
atmosphere is more dense, slowing the light more
Rays from the bottom of the Sun have a greater angle of incidence
Flattened Sun
Mirages A virtual image that forms as a result of refraction
and total internal reflection in Earth’s atmosphere This is the result of light travelling through
different air temperatures The index of refraction decreases as air gets
warmer, causing the light to bend farther away from the normal
Total internal reflection occurs in the hottest layer, usually on the Earth’s surface
The ray travels back through to the cooler air and bends back toward the normal
Mirages When the light reaches our eyes, we
think it travelled in a straight line This results in an image of the sky
appearing to be on the pavement or sand
Mirages
Shimmering Also caused by light refracting through
different air temperatures Air closer to the lake is warmer, so the
light refracts in the same pattern as it does near hot pavement
Total internal refraction occurs in the lowest, warmest layer causing multiple virtual images on the water’s surface
Shimmering
Rainbows Rainbows are a result of the dispersion of
white light into its 7 colour components Remember: red light is refracted less
than violet due to its speed ROYGBIV Rainbows are produced by water droplets3 steps:Dispersion of white light by the rain dropPartial internal reflection at the back of the
rain dropRefraction of the light exiting the rain drop
Rainbows Our eyes see the final refraction, and
projects these rays backwards to form a virtual image of a rainbow
You can only see a rainbow when the sun is behind you
Rainbow
Picture CreditsApparent Depth
http://wpcontent.answers.com/wikipedia/commons/6/62/Pencil_in_a_bowl_of_water.png
Water Mirageshttp://img2.blogabond.com/UserPhotos/1937/580/
WaterMirage.jpghttp://www.kookynet.net/media/k3832_p-mirage-
simpson.jpgMirage Diagramhttp://image.tutorvista.com/content/light-refraction/
mirage.jpeg
Picture CreditsMoon shimmeringhttp://www.boatnerd.com/news/newsthumbs/
images/Moon-10-25-04-dcr.jpghttp://jamminwithjay.com/images/
080612_alaska/Alaska_074.JPGRainbowhttp://www.alaska-in-pictures.com/data/media/
13/rainbow-over-the-muldrow-glacier_1127.jpg
http://www.rebeccapaton.net/rainbows/formatn.htm