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Example 9.1: Conversion of Pressure Units

The United States National Weather Service reports pressure in both inches of Hg and millibars. Convert a pressure of 29.2 in. Hg into:
(a) torr
(b) atm
(c) kPa
(d) mbar

Solution

This is a unit conversion problem. The relationships between the various pressure units are given in Table 1.

\(\mathrm{inHg}\) \(= 2.54\ \mathrm{mmHg}\)


\(P\) \(= 29.2 \cdot \mathrm{inHg}\)

\(\ \ \ =29.2 \cdot 2.54\ \mathrm{mmHg}\)

\(\ \ \ =74.2\ \mathrm{mmHg}\)


\(P\) \(= 74.2\ \mathrm{mmHg}\)

\(\ \ \ =74.2\ \mathrm{mmHg}\)


\(P\) \(= 74.2\ \mathrm{mmHg}\)

\(\ \ \ =0.0976\ \mathrm{atm}\)


\(P\) \(= 0.0976\ \mathrm{atm}\)

\(\ \ \ =9.89\ \mathrm{kPa}\)


\(\mathrm{mbar}\) \(= 100\ \mathrm{Pa}\)


\(P\) \(= \dfrac{P}{\mathrm{mbar}}\mathrm{\ \mathrm{mbar}}\)

\(\ \ \ =\dfrac{9.89\ \mathrm{kPa}}{100\ \mathrm{Pa}}\mathrm{\ \mathrm{mbar}}\)

\(\ \ \ =\dfrac{9.89\ \mathrm{kPa}}{100\ \mathrm{Pa}}\mathrm{\ \mathrm{mbar}}\)

\(\ \ \ =98.9\mathrm{\ \mathrm{mbar}}\)