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Purpose of this Minilab

Purpose of this Minilab. Learn about and determine the coefficient of thermal expansion. Determine the lowest possible temperature (absolute zero). Thermal Expansion in one Dimension (Length Change). change in temperature. change in length. initial length.

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Purpose of this Minilab

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  1. Purpose of this Minilab • Learn about and determine the coefficient of thermal expansion. • Determine the lowest possible temperature (absolute zero).

  2. Thermal Expansion in one Dimension (Length Change) change in temperature change in length initial length coefficient of thermal expansion (depends on the material)

  3. Thermal Expansion Apparatus length gauge Thermistor (resistance depends on temperature) 3 different metal tubes

  4. Inserting the Metal Tube Gauge pin Angle bracket Attach thermistor. Tighten screw. Insert metal pin as shown. Tighten screw.

  5. Cover Thermistor with Insulation, Attach DMM.

  6. Thermistor • Thermistor has resistance that changes with temperature. • Conversion scale is on the thermal expansion apparatus. • You need to interpolate to get temperature for values in between • those that are listed. • Interpolation procedure is shown in manual.

  7. Steam Generator ( Change Temperature of Metal Rod) Rubber hose goes to metal rod. Second outlet should be plugged. Remove plug and fill in sufficient amount of water. Dial lets you change the amount of steam generated.

  8. Steam from steam generator Put small cup here to catch condensed water. Lift this end up so that condensed water runs out the other end of the metal rod.

  9. Measurement • Set gauge to “zero” at room temperature. • Start steam generator. • Watch resistance (to monitor temperature) and length expansion. • Record highest temperature (lowest resistance) measured. • Record maximum expansion measured. • Calculate the coefficient of thermal expansion. Note: Due to time delays relating to thermal conduction the highest temperature and the largest expansion may not happen exactly at the same time.

  10. Absolute Zero Temperature For ideal gases (gases at low pressure) Pressure Temperature (in degrees Kelvin) Volume Universal gas constant Amount of gas in moles

  11. Absolute Zero Temperature The ideal gas law implies: As the gas is cooled more and more, the pressure sinks (if the volume of gas and the amount of gas is kept constant).  For P = 0 the lowest possible temperature is reached.

  12. Estimating Absolut Zero Temperature • Keep volume of gas constant. • Keep amount of gas constant. • The P versus T graph is a straight line with slope nR/V. • Plot T in degrees Celsius. • Determine lowest possible T in Celsius. • Determine the uncertainty in lowest T. P 0 T Measuring at least two points lets you extrapolate to P=0.

  13. Determining the Pressure of the Gas Inside the Sphere Gauge Pressure = Pressure inside the sphere – Pressure outside the sphere Read gauge Measure with barometer Varying the Temperature of the Gas in the Sphere Dip the sphere into boiling water (to get approx. 100 Celcius). Dip the sphere into ice water (to get approximately 0Celcius). Use the same sphere at different temperatures. (the amount of gas in different spheres may not be the same).

  14. Estimating the Uncertainty in Lowest T P 0 T Possible range of lowest temperature.

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