PDF chapter test TRY NOW
Get a square piece of cardboard of size 6-8 cm. Make two holes. Thread a string through the two holes. Draw/ paste a cage on one side of the cardboard and
a bird on the other side. Twist the string and make the card twirl rapidly. Do you see the bird in the cage?
Bird in cage
, the bird in the cage .
As a result, an image's impression lasts in the retina for around of a second.
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