Boyle's Law/Pressure in Gases

PHY 100 & 103

Students determine the relationship between pressure and volume of a confined ideal gas at constant temperature. To do this, the volume of air trapped in a capped syringe is measured while applying a series of increasing forces (the push) to the plunger. Newton’s Laws tell us that if the plunger is not accelerating (in fact, it won’t be moving at all when you take your data), then the net force on it must be zero. For any particular steady push on the plunger, there will be one position where it comes to rest and remains in that position. To find this “ equilibrium position”, we add weight and push gently on the plunger to break static friction and let it rebound. With the piston in that position, the forces exerted downward on the piston must be equal to the upward force of air on the plunger. Knowledge of the upward air force on the plunger allows the calculation of the contained air Pressure as the upward force on the plunger divided by the surface area over which it makes contact with the tip of the plunger.

Equipment

Notes

The large slotted masses needed include one of each of the following : 2kg, 1kg, 1/2kg. Hanging set up for decreasing internal pressure is seldom used, but check with supervisor/instructor for choice between set up's pictured and whether a caliper will be used. Don't put out caliper or hang apparatus unless told to. When simply placed on the table, cork must face down and not cause instability. Adjust the syringe body in lower block to prevent teetering on cork. See supervisor regarding occasional cleaning of syringe. Syringe in hanging set-up must be vertical, have ears resting on top of lower clamp, and fit loosely in both clamps.

Along with the initial apparatus set-up, supply a sufficient number of the appropriate paper procedure handouts for all of the lab sections that will use the set-up over the course of the week. Print the PDF, duplicate to double-sided pages, staple, and leave pile on instructor's table prior to first use of set-up.