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 Depth

OBJECTS 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 Credits

Apparent 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 Credits

Moon 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