'Torr' is a unit of ________.
- A.Power
- B.Pressure
- C.Energy
- D.Force
Show answer
Correct answer: B. Pressure
Explanation
The correct answer is B, Pressure. The torr is a unit of pressure named after Evangelista Torricelli, the Italian scientist who invented the mercury barometer in 1643. One torr is the pressure of a one-millimetre column of mercury, so 1 torr = 1 mm Hg, and it equals about 133.3 pascal. Normal atmospheric pressure at sea level is 760 torr, which is the same as 760 mm Hg, 1 atmosphere or 101,325 pascal. The pascal is the SI unit of pressure, one newton per square metre, but the torr and mm Hg are still used for blood pressure and vacuum work. A, Power, is measured in watt, with horsepower as the older unit. C, Energy, is measured in joule, with calorie and electron-volt as other units. D, Force, is measured in newton, or dyne in the CGS system. Exam tip: pressure units are pascal, bar, atmosphere, torr and mm Hg; 760 torr = 1 atm.