Torr
The torr is a unit of pressure used in the measurement of vacuum and atmospheric pressure. It's named after the Italian physicist Evangelista Torricelli, who is credited with inventing the barometer in the 17th century. Here are some key points about the torr:
- Definition: One torr is defined as 1/760th of a standard atmosphere. This means that standard atmospheric pressure, which is about 101,325 pascals (Pa) or 760 millimeters of mercury (mmHg) at sea level, is equivalent to 760 torr.
- Relation to Other Units:
- The torr is closely related to the millimeter of mercury (mmHg) unit. By definition, 1 torr is approximately equal to 1 mmHg, though there is a slight difference: 1 mmHg is defined as exactly 133.3223684 pascals, whereas 1 torr is defined as exactly 101,325/760 pascals (which is approximately 133.322 pascals).
- In the International System of Units (SI), the standard unit of pressure is the pascal. Therefore, 1 torr equals about 133.322 pascals.
- Usage: The torr is commonly used in fields like vacuum technology, where pressures lower than atmospheric pressure are important. It's also used in some medical and scientific contexts, such as blood pressure measurements and gas law experiments.
- Conversion: To convert torr to other units of pressure, you can use the following approximate conversions:
- 1 torr ≈ 133.322 pascals (Pa)
- 1 torr ≈ 1.33322 millibars (mbar)
- 1 torr ≈ 0.01934 pounds per square inch (psi)
The torr is a practical unit for measuring pressure, especially in applications where working with fractions of an atmosphere is more convenient than using pascals or other SI units.