(a) Draw a labelled diagram of a vacuum flask. Explain how its construction minimizes heat exchange with the surroundings.

(b) State Boyle's law. A thread of mercury of length 15cm is used to trap some air in a capillary tube with uniform cross- sectional area and closed at one end with the tube vertical and the open end uppermost, the length of the trapped air column is 20cm. Calculate the length of the air column when the tube is held:

(i) Horizontally ; (ii) vertically with the open end underneath. [Atmospheric pressure = 76cm Hg]

(c) Explain why it is not advisable to sterilize a clinical thermometer in boiling water at normal atmospheric pressure.