Question

A pressure of 1 torr is equal to ______

• A. 1m H$_2$O
• B. 1kgf/m$^2$
• C. 1mm Hg
• D. 1 N/m$^2$

Hint:

Keep standard conversion factors memorized:
\[ 1 \text{ atm} = 760 \text{ mm Hg} = 760 \text{ torr} = 10.33 \text{ m H}_2\text{O} = 1.033 \text{ kgf/cm}^2 = 1.01325 \text{ bar} \]
These conversions are essential for solving fluid flow and thermodynamics problems quickly.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for the definition or equivalent physical unit of 1 torr of pressure.
This is a standard unit conversion question under the topic of fluid mechanics and process calculations.

Step 2: Key Formula or Approach:
Pressure is defined as force per unit area.
Various units are used to measure pressure, including Pascals (\( \text{N/m}^2 \)), atmospheres (atm), bar, millimetres of mercury (mm Hg), and torr.
The standard atmospheric pressure at sea level is defined as:
\[ 1 \text{ atm} = 760 \text{ mm Hg} = 760 \text{ torr} = 101,325 \text{ Pa} = 1.01325 \text{ bar} \]

Step 3: Detailed Explanation:

• Torr and mm Hg: The torr is a non-SI unit of pressure designed to be equal to the fluid pressure exerted by a millimetre of mercury.
Historically, 1 torr was defined as exactly \( 1 \text{ mm Hg} \).
Thus, \( 760 \text{ torr} = 760 \text{ mm Hg} \).

• Other Options:
\( 1 \text{ mm Hg} \) is equivalent to approximately \( 133.322 \text{ Pa} \) or \( 133.322 \text{ N/m}^2 \).
Therefore, \( 1 \text{ torr} \neq 1 \text{ N/m}^2 \).
\( 1 \text{ kgf/m}^2 \) is equivalent to \( 9.80665 \text{ Pa} \), which is different from 1 torr.
\( 1\text{m H}_2\text{O} \) is equivalent to about \( 9806.65 \text{ Pa} \) or \( 73.5 \text{ mm Hg} \).


Step 4: Final Answer:
By physical definition, a pressure of 1 torr is exactly equal to 1 mm Hg.