Boyle's law: pressure and volume of a gasStarter example
A starter example, adapted by LABKickstart from the OpenStax College Physics for AP Courses Lab Manual and shared under CC BY 4.0. It is not a classroom submission from a teacher on Benchtop.
Trap a fixed amount of air, squeeze it with known weights, and measure how its volume falls as the pressure rises. The area under the resulting curve is the work done on the gas.
Materials
- Boyle's law apparatus, or a large sealed syringe with a piston and a stable platform
- A set of known masses, or books and bricks that can be massed
- Lab scale
- Metre rule or the syringe's own volume scale
- Graph paper
Procedure
- Seal a known starting volume of air in the syringe with the piston free to move.
- Record the volume with no load, and work out the pressure from the atmosphere alone.
- Add a known mass to the piston, wait for it to settle, and record the new volume.
- Repeat for at least five loads, each time computing pressure as force over piston area plus atmospheric pressure.
- Tabulate pressure against volume and also compute the product of the two for each row.
- Plot pressure against volume and estimate the area under the curve between your first and last points.
Expected results
The product of pressure and volume stays roughly constant across the whole run, which is Boyle's law. The pressure against volume plot is a curve, not a line. The area under it is the work done compressing the gas, and it should come out close to the work recovered on expansion if you let the loads off one at a time. Drift in the product usually means the seal leaks or the gas has warmed.
Safety
Do not load the piston past the apparatus rating, and never point a loaded syringe at anyone: a seal that lets go fires the piston. Stack masses so they cannot topple, and release the load slowly rather than lifting it all at once.
Source
Adapted from OpenStax, College Physics for AP Courses Lab Manual (CC BY 4.0). Access for free at openstax.org. AP is a trademark registered by the College Board, which was not involved in and does not endorse this adaptation.
Downloads
- OpenStax Lab 17: GasesPDF510 KBDownload
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