The depth of a bucket filled with water seems to be less than its actual depth. Name the phenomenon responsible for this?

The depth appears to be less because of refraction of light. Light rays bend as they move from water to the air. When the light ray from water reaches our eye, the eye traces them back as straight lines (shown as dashed lines) which intersect at a higher position than where the actual rays originated. This causes the depth of a bucket to appear higher and we cannot see the actual depth of the bucket.

The figure below illustrates the same.



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