Measurement of Pressure Manometer – Physics Class 9

Measurement of Pressure Manometer — Class 9 Physics Lecture Summary

Lecture Overview

While a barometer measures the pressure of the open atmosphere, this lecture introduces the Manometer, an instrument designed to measure the pressure of enclosed gases (like in a cylinder or a gas pipe).

Main Concepts Explained by the Teacher

The teacher demonstrates a U-shaped tube filled with a liquid (usually water or mercury). One end is connected to the gas supply, and the other end is open to the atmosphere. The difference in the liquid levels in the two arms indicates the difference between the gas pressure and the atmospheric pressure.

Important Definitions and Terms

• Manometer: A U-tube device used to measure the pressure of enclosed gases relative to atmospheric pressure.
• Gauge Pressure: The difference between absolute pressure and atmospheric pressure ($P =

ho g h$).

Key Points and Lists from the Lecture

• If the liquid is pushed down on the gas side, the gas pressure is greater than atmospheric pressure.
• If the liquid is pushed down on the open side, the atmospheric pressure is greater.
• Gas Pressure = Atmospheric Pressure + $h

ho g$ (if gas side is lower).

What Students Should Remember

Well, A manometer does not directly give the absolute pressure. It gives the difference in pressure ($\Delta P$). Make sure you remember to add the atmospheric pressure back in if calculating total absolute pressure.

Textbook, Notes, and Practice Links

• Textbook: Physics Full Textbook
• Video Notes: Notes for this Lecture

Final Recap & Board Exam Notes

The manometer completes the student's toolkit for measuring pressure. 9th class students now understand how both open environmental pressures and closed industrial gas pressures are quantified in the lab.

• This is a total lifesaver for 9th class Punjab Board and FBISE exams.*

This notes format is exactly what examiners look for in FBISE 9th class papers.