Question

why the paper get burn ​

Answer 1

Answer:

When sun rays fall on the convex lens they get converged to a point. ... These rays surely have heat energy and they get accumulated in that point. When the amount of rays have accumulated enough so as to reach the ignition temperature of paper, the paper catches fire. Thus the paper is burnt.

Explanation:

For example, when paper is burned oxygen from the air combines with carbon and hydrogen in the paper turning some of it into carbon dioxide and water vapor, which waft away with carbon particulates in the smoke. This, not surprisingly, leaves the solid ash leftover lighter than the original paper