What happens to compass needles at the Earth's poles ?

What direction compass needle points at poles ? Which needle to be used at poles ?

What happens in systole?

What happens to air on heating it?

What happens to air on cooling it?

A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.

What happens if there are no decomposers on earth?

What happens if seeds are not dispersed?

What happens when a hot needle is placed between two match sticks placed on the surface of water?