Question

What is a manometer? How does it show whether the pressure inside a vessel connected to one arm of it, is lower or above the atmospheric pressure?

Answer 1

A manometer is a simple pressure gauge that measures differences in pressure at the two ends of the apparatus.
The manometer is a U shaped tube containing water whose one limb is dipped in vessel and vessel is tightly covered with a plastic sheet. U shaped tube has two limbs one towards the vessel and the other is opened to the atmosphere.
Now if the level of water toward atmospheric open limb is more than the level of water in limb towards apparatus end then the liquid is said to be at a higher pressure than the atmosphere. And if the level of water toward atmospheric open limb is less than the level of water in limb towards apparatus end then the liquid is said to be at a lower pressure than atmospheric pressure.