The correct answer is: D. difference of pressure between two points.
A differential manometer is a device used to measure the difference in pressure between two points. It is typically used to measure the pressure drop across a valve or orifice, or to measure the pressure differential between two fluid streams.
A differential manometer consists of two U-shaped tubes connected to each other at the bottom. The tubes are filled with a liquid, such as mercury or water. The pressure difference between the two points is measured by the difference in the height of the liquid in the two tubes.
The differential manometer is a simple and accurate device for measuring pressure differences. It is widely used in a variety of industries, including the chemical, oil and gas, and water treatment industries.
Here is a brief explanation of each option:
- Option A: Pressure in pipes, channels, etc. This is not the correct answer because a differential manometer is used to measure the difference in pressure between two points, not the pressure at a single point.
- Option B: Atmospheric pressure. This is not the correct answer because a differential manometer is used to measure the difference in pressure between two points, not the atmospheric pressure.
- Option C: Very low pressure. This is not the correct answer because a differential manometer can be used to measure a wide range of pressure differences, including very low pressure differences.
- Option D: Difference of pressure between two points. This is the correct answer because a differential manometer is specifically designed to measure the difference in pressure between two points.