THERMAL PHYSICS LABORATORY:
INVESTIGATION OF ADIABATIC PROCESSES IN AIR
This experiment has two parts. In the ﬁrst, you will use a dynamic method to measure the ratio of the speciﬁc heat capacities of air and, in the second, you will investigate the behaviour of gas undergoing an expansion that is approximately adiabatic and ‘partially reversible’ – somewhere between the two limits of a completely irreversible (free) and perfectly reversible expansion. The air can be considered an ideal gas. DESCRIPTION AND EXPERIMENTAL PROCEDURE
PART I: Determination of γ for Air
Motion of Steel ball
R Tap ubber mat
The apparatus consists of a large vessel into which a long vertical transparent tube is ﬁtted. The diameter of the tube is such that a steel ball just ﬁts into the tube, so that the ball can freely move in the tube but the air in the vessel and lower part of the tube is nearly isolated from the outside atmosphere after the ball is inserted. This vertical tube has been made with precision and is an expensive item – please treat it with respect and handle it with care!
1. Set up the apparatus with the rubber mat lying in the bottom of the vessel and the tap closed.
2. Drop the ball into the glass tube. The ball will oscillate with simple harmonic motion on the air cushion formed by the enclosed volume of air. Record the time for ten oscillations or so, making a note of the number of oscillations. If the ball does not move freely in the tube, carefully clean the inside of the tube and the surface of the ball and try again (the ﬁt of the ball in the tube is so precise that even small amounts of dirt can hinder the free motion of the ball). 3. Repeat step 2 about ten times, to verify that the period of the motion T is constant, and to improve the accuracy of your ﬁnal value for T. 4. Measure the mass m and diameter d of the steel ball and record this information together with the corresponding uncertainties.
5. Make note of the volume of...
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