Alternative text (alt text) is meant for readers who cannot see an image, such as blind readers and readers who use a text or mobile browser. It should summarize an image's purpose, and should not duplicate its caption. Every image should have alt text, except for purely decorative images, which should instead have "|alt=|link=".
Free electron model
The following table shows images and captions on the left, and alt text and captions on the right: the right column is what a visually impaired reader will hear. This table was computed from the copy of Free electron model cached on 12 May 2013 at 20:22.
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In three dimensions, the density of states of a gas of fermions is proportional to the square root of the kinetic energy of the particles.
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Plane wave traveling in the x-direction
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Traveling plane waves
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 | Wikipedia book
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 | Category
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 | Portal
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