2LB_Lab_3_SpecHeatSol5

2LB_Lab_3_SpecHeatSol5 - Specific Heat of Solids (*Includes...

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Specific Heat of Solids (***Includes Pre Lab Assignment) Objective: This week we will measure the specific heat of several solid samples. The specific heat refers to the amount of heat that a material can store internally in its atomic, electronic and molecular motions. The specific heats will be measured using the latent heat of vaporization for liquid nitrogen (LN 2 ). Heat removed from the sample in cooling from room temperature to LN 2 temperature (77 K) will lead to the vaporization of nitrogen. Apparatus 1. Styrofoam cups (to serve as a Dewar) 2. Samples: Two metal samples (aluminum and iron) and a piece of rock. 3. Liquid nitrogen, LN 2 4. Weighing Scale 5. Resistor 6. Rod and stand to support resistor 7. Power supply 8. Dual Digital voltmeter/ammeter 9. Large room thermometer 10. Computer with Data Studio software 5 6 1 4 A The Apparatus V 7

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The Physics The amount of thermal energy ( heat ) required to raise the temperature of an object is determined by the heat capacity of the object. The heat capacity is defined as the amount of energy required to raise the temperature of an object by one degree Kelvin. T C Q Δ = where Q is the amount of heat energy, C is the heat capacity, and Δ T is the change in temperature. Specific Heat The heat capacity clearly depends on the mass of the object we are considering. It is convenient to introduce a quantity that does not depend on the mass of the object, but only on the material of the object. This quantity is the specific heat , which is defined as the heat capacity per unit mass. Twice as much material will have twice as much heat capacity, but the specific heat will be the same for all objects made of the same material. The specific heat is defined as c = C / m The calorie is a unit of heat (energy) defined as the amount of heat required to raise one gram of water by one degree Celsius (note that a change in temperature by one degree Celsius is the same as a change by one degree Kelvin). Thus, the specific heat of water is c water = 1.00 cal / g K = 4186 J / kg K Latent Heat When a substance changes state (solid to liquid, or liquid to gas, or solid to gas) there will be a transfer of heat associated with the change of internal energy. The heat energy absorbed by the material goes to breaking the bonds (potential energy) that hold the atoms/molecules together to form the solid or liquid. There is no change in temperature associated with the change of state . The heat of transformation depends on how much material is present, so Q = mL where m is the mass of the material, and L is the Latent Heat, or Heat of Transformation. For example, the solid (ice) to liquid transformation of water has a latent heat of L = 3.33x10 5 J/kg = 79.7 cal/g. Note, that the temperature of the ice remains at 0 o C, while the heat is being absorbed by the ice.
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This note was uploaded on 01/11/2010 for the course PHYS 2b taught by Professor Clare during the Fall '07 term at UC Riverside.

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2LB_Lab_3_SpecHeatSol5 - Specific Heat of Solids (*Includes...

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