At a research observatory located 4500m above sea level, the atmospheric pressure is observed to be 0.70atm. A compressed–air cylinder is being filled at this site so that its internal gauge pressure just reaches 1.8MPa when the valve is closed.
(i) Compute the absolute pressure of air inside the cylinder at the filling site in Pascal.
(ii) Keeping the temperature unchanged, the cylinder is later brought down to sea level where the atmospheric pressure is 1.013×105Pa. Calculate the new gauge pressure that would be indicated by the same gauge.
(iii) Explain briefly why the gauge reading changes even though the mass of air inside the cylinder remains the same.