1. The problem statement, all variables and given/known data To construct a barometer, a tube of length 1m is filled completely with mercury and is inverted in a mercury cup. The barometer reading on a particular day is 76cm. Suppose a 1m tube is filled with mercury up to 76cm and then closed by a cork. It is inverted in a mercury cup and the cork is removed. The height of mercury column in the tube over the surface in the cup will be a)zero b)76cm c)>76cm d)<76cm 2. Relevant equations 3. The attempt at a solution Since the tube has been partially filled thus air is present in it. When it is inverted the air exerts a pressure on the mercury filled in it. Also the atm .pressure is exerted at the surface of mercury present in cup. But which one is greater?