Textbook Problem

When air pressure increases, what happens to the mercury in the tube?

To determine

The change in the mercury of the tube in response to the increase in air pressure.

Answer to Problem 1FQ

The mercury inside the tube will be forced to rise up in response to an increase in the air pressure.

Explanation of Solution

Figure 4.1 demonstrates a simple mercury barometer that measures the barometric pressure, which was devised by one of Galileo’s students, Evangelista Torricelli. The device was constructed on the basis of an experiment with mercury.

Torricelli took a long glass tube with a closed end and filled it with mercury. It was then upturned into an open pan of mercury. In response to this, mercury within the tube drops till it reaches a height of around 76 centimeters above the mercury kept  in the pan, leaving a vacuum bubble at the closed top end of the tube.

The pressure applied on mercury kept in the open pan by the atmosphere was equivalent to the pressure from mercury that is trying to drain from the tube. With an increase in the atmopsheric pressure, mercury in the tube is then forced up to a higher level. When the atmopheric presssure declines, the level of the mercury column also drops proportionally.