Manometer


 
 
Concept Explanation
 

Manometer

Measuring Liquid Pressure: The Manometer: A manometer is a simple device used to measure liquid pressure. It has a U-shaped glass tube which is fixed to a wooden board having a scale. The U-tube is filled with colored water such that its limbs are half filled. One end of the U-tube is open. The other end is fixed to rubber tube which in turn is connected to a thistle funnel. This improvised apparatus is called as manometer.

Take this apparatus and cover the mouth of thistle funnel with a tight thin rubber sheath taken from a balloon. If you press the rubber sheath lightly with your fingers, the pressure on it increases. Due to this the water level in limb A will go down and in limb B will go up. You can read the difference in water levels on the scale. This is a measure of pressure exerted on the rubber sheath

Measuring Liquid Pressure In Different Directions At The Same Depth: Now keeping the funnel at the same level change the direction of mouth of funnel to sideways in fig. (b). The rise in level of water in U tube remains the same. This shows that liquid pressure does not change. This proves that at the same depth a liquid exerts equal pressure in all directions. Liquid pressure increases with depth.

Consequences of Liquid Pressure:

1. We know that the pressure exerted by water in the oceans increases with depth. Very deep down the pressure is enough to crush the human body. That is why deep-sea divers wear special suits, which can withstand such high pressures and prevent their bodies to crush.

2. When deep sea fishes are brought up to the surface of sea, their bodies flow at a very high pressure. At the surface of sea, the pressure outside suddenly decreases. Due to this difference in pressure their bodies burst open. Submarines are built of hard thick sheets of metal to withstand the high pressure under water.

Sample Questions
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Question : 1

Which of the following are correct :

(a) The pressure exerted by water in the oceans increases with depth.

(b) The pressure exerted by water in the oceans decreases with depth.

Right Option : A
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Question : 2

The pressure exerted by water in the oceans _________________ with depth.

Right Option : B
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Question : 3

Which of the following are correct :

(a) A manometer is a simple device used to measure liquid pressure.

(b) A manometer is a simple device used to measure temperature.

Right Option : A
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