Question

how we will find the square root of 7 on the number line

Answer 1

On the number line, draw a perpendicular line of length 1 unit from point (2,0).
Join the tip of the perpendicular line and origin. The line you got now has a length of
$\sqrt{ {2}^{2} + {1}^{2} } = \sqrt{5}$
Now project this length on the number line by drawing an arc using a compass.
Again draw unit perpendicular and repeat the procedures until you get
$\sqrt{ { \sqrt{5} }^{2} + {1}^{2} } = \sqrt{6} \\ \sqrt{ { \sqrt{6} }^{2} + {1}^{2} } = \sqrt{7}$