phyics help needed!

A cylinder containing air at pressure of 1.0 x 10^5 Pa. The length of the air column in the cylinder is 80 mm. The piston is pushed until the pressure in the cylinder rises to 3.8 x 10^5.

a) Calculate the new length of the air column in the cylinder, assuming that the temperature of the air has not changed.

b) The apparatus is used as a thermometer. Describe how two fixed points, 0C and 100C, and a temperature scale could be marked on the apparatus.
c) Describe how this apparatus could be used to indicate the temperature of a large beaker of water.

AIGHT. I GIVE UP ON THIS QUESTION. Anyone got any idea??

thnx.

A cylinder containing air at pressure of 1.0 x 10^5 Pa. The length of the air column in the cylinder is 80 mm. The piston is pushed until the pressure in the cylinder rises to 3.8 x 10^5.

a) Calculate the new length of the air column in the cylinder, assuming that the temperature of the air has not changed.

With temperature constant, volume is inversely proportional to pressure. As the cross sectional area of the cylinder is constant, the volume of the cylinder is proportional to the length. So if the pressure increases by a factor of 3.8, the 80mm (=0.08m) tube will be reduced by that factor, giving a new length of 21mm (2s.f.).

b) The apparatus is used as a thermometer. Describe how two fixed points, 0C and 100C, and a temperature scale could be marked on the apparatus.

If you keep the pressure inside constant by allowing the tube to expand, the volume and therefore length will be proportional to the temperature of the gas in Kelvin. You would put it at 0 C and mark on the expansion, and put it at 100 C and mark on that as well. You should be able to draw the rest on from those two by using suitable divisions. (I think this is right?!)

c) Describe how this apparatus could be used to indicate the temperature of a large beaker of water.

Submerge the apparatus in the water, keeping it near the surface (to avoid a change in external pressure as the weight of the water will cause a lower than true temperature reading to be shown at a large depth), and allow it to expand or contract. Read off the temperature from the scale you made?

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I haven't done this physics for a whole year. SO I may be wrong.

phyics help needed!

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