Question

which is the principal on which sundial is based​

Answer 1

The sundial works on the principle that when the sun is at highest point in the sky the image of an object formed by its light is smallest and when it is at the lowest point the image formed is the longest.

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Answer 2

Answer:

The sundial measures "apparent solar time." This means that noon on the sundial is when the sun is on the "meridian", the imaginary line that divides the east half of the sky from the west half.

Explanation:

The sundial works on the principle that when the sun is at highest point in the sky the image of an object formed by its light is smallest and when it is at the lowest point the image formed is the longest. The most major drawback of sundial is that it cannot be used in the night.