Question

which lense is used to burning paper​

Answer 1

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Convex lens

Thus Convex lens is used to burn paper.

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Answer 2

A convex lens is used to burn paper. As it converges light.

When a piece of paper is placed at a distance equal to the focal length of the lens from the lens, light rays (usually sun rays) will hit the lens from the other side and converge at a point on the paper. This leads to the heating of that point, and ultimately results in it burning.