Questions: Select all of the following that correctly describe manometers. They are straight tubes closed at one end. They are U-shaped tubes. They are used to measure the pressures of gases. The difference in the fluid levels is a measure of the pressure difference. The liquid in a manometer must be mercury. The difference in the fluid levels is a measure of the pressure.

Solution Steps

1. They are straight tubes closed at one end.
   This statement is incorrect. Manometers are typically U-shaped tubes, not straight tubes closed at one end.

2. They are U-shaped tubes.
   This statement is correct. Manometers are commonly U-shaped to allow for the measurement of pressure differences.

3. They are used to measure the pressures of gases.
   This statement is correct. Manometers are used to measure the pressure of gases by comparing it to a known pressure.

4. The difference in the fluid levels is a measure of the pressure difference.
   This statement is correct. The difference in fluid levels in the two arms of a manometer indicates the pressure difference between the gas and the reference pressure.

5. The liquid in a manometer must be mercury.
   This statement is incorrect. While mercury is commonly used due to its high density, other liquids can also be used depending on the application.

6. The difference in the fluid levels is a measure of the pressure.
   This statement is correct. The difference in fluid levels can be used to determine the pressure of the gas being measured.

Final Answer