# Thermodynamics: Determine pressure in the tank of a manometer

• Engineering
• mhrob24
In summary, the video explained the concept of pressure in a tank and how it relates to the pressure at a specific point. The professor mentioned that while the pressure at point A is technically not exactly equal to the pressure in the tank due to the weight of the gas in the connecting tube, this difference is negligible due to the lower density of gas compared to liquid. However, for precise calculations, the weight of the gas in the connecting tube above point A should be included. The concept of varying pressure with depth, similar to the ocean, was also discussed and the effects of gas density on this were mentioned.

#### mhrob24

Homework Statement
Find the pressure (Pt) in the tank of the manometer
Relevant Equations
P= W/A = density x gravity x height
I was watching a YT video getting prepared for class this coming semester, and in the video, this diagram of a manometer was drawn (see image at end of message). The professor stated that the pressure in the tank (Pt) is = to the pressure at point A. Following this, he said that technically speaking, it wasn’t EXACTLY equal because of the weight of the gas in the portion of the tube connected to the tank, but because the density of the gas is much smaller than the density of the liquid, it would make a trivial difference.

I THINK I get what he’s saying but I want to be sure. So basically, the “tank” here is considered to be just the square tank…..not including the connection tube (even though that tube is exposed to the gas in the tank). So in all reality, if you wanted to truly calculate the EXACT pressure at point A, you would have to include the weight of the gas in that portion of the tube above point A. Is this correct? That’s the only way I can make sense out of what was said in the video…

I believe that you are both correct.
Just like it happens in the ocean, the pressure inside the tank will vary with the "depth" at which the point we want to measure is sumerged in the mass of gas, plus the static pressure inside the tank.

You may need to analyse the hydrostatic pressure change with height in both the liquid and the gas. The gas has variable density which will make it interesting.

## 1. What is thermodynamics?

Thermodynamics is the branch of physics that deals with the study of energy and its transformations, particularly in relation to heat and work.

## 2. How is pressure determined in a manometer?

Pressure in a manometer is determined by measuring the height difference between the two columns of liquid in the manometer. The pressure difference between the two columns is equal to the difference in height multiplied by the density of the liquid and the acceleration due to gravity.

## 3. What is a manometer used for?

A manometer is used to measure the pressure of a gas or a liquid in a closed system. It is commonly used in industries such as chemistry, engineering, and medicine.

## 4. How does a manometer work?

A manometer works by using a column of liquid, typically mercury or water, to measure the pressure of a gas or a liquid. The liquid in the manometer will rise or fall depending on the pressure difference between the two ends of the manometer.

## 5. What are the different types of manometers?

There are several types of manometers, including U-tube manometers, well-type manometers, and inclined-tube manometers. Each type has its own specific use and advantages, but they all work on the same principle of measuring pressure using a column of liquid.