Lord Kelvin (A.K.A. William Thompson)
June 26, 1824 ~ Dec. 17, 1907
(Image thanks to: http://www.chemie.uni-bremen.de/stohrer/biograph/kelvin.htm)
Temperature and Heat Transfer

Introduction

In this lab the class split into groups to work on the experiments outlined on the physics class web site. The purpose of these experiments was to learn about the abilities of different states of matter (gas, liquid, and solid) in the transfer of heat with the use of a temperature probe and a heat pulsar. The understanding of the concepts of kinetic theory, temperature, heat, thermal energy, and specific heat are also important.

     The kinetic theory tells us that all matter is made up of individual particles (atoms or molecules) that are always in motion. A gas contains molecules with a wide range of speeds and are located far away from each other. A liquid has molecules closer together and have the smallest range of speeds. For any of the three states of matter the solid state of a compound has molecules that are the closet together and have the smallest range of speeds. The kinetic energy of these particles moving at random within an environment is known collectively as thermal energy. When this energy is transferred to another system it is called heat. The degree of heat that a body of matter is said to contain is temperature. Specific heat is the amount of thermal energy to change one kilogram of a certain substance one degree Kelvin; each species having a unique specific heat.
 
 

      The first experiment done in class had a sealed chamber of Freon-115 heated to its critical temperature. Nearing the is temperature the liquid within the chamber showed turbulence and was vaporized. When the Freon-115 was allowed to cool the vapor became turbulent and turned opaque. A few seconds later, to our surprise, the liquid state started to reappear!

       In lab on Tuesday, we worked on a series of experiments that were designed to help us understand how kinetic energy in the form of heat is transferred from one group of molecules to another. First, a probe was calibrated with the aid of Logger pro software using cold water and then hot water. The water was obtained from the sink in the bathroom just outside of the classroom. The cold water was determined to have a temperature of 15 C and the hot water had a temperature of 36 C. The next part of the experiment was to predict the amount of time the probe would take to reach equilibrium when it was submerged into ice water. Our group's estimate was somewhere between 60 and 45 seconds. The actual time measured using the computer program was 50 seconds. Next, the time the probe took to equilibrate with the air from the cold water was estimated. Our group predicted the same amount of time as in the last test: between 60 and 45 seconds. What we found using Logger Pro software was quite different than what we had expected, approximately 120 seconds. This was more than double the period the probe had taken to reach equilibrium with the water. The professor came around to each group and asked us why we thought that the probe had such different reactions to the two different states of matter air Vs. water. The air (as mentioned above) had particles of matter that air far apart from one another and a wide range of collision speeds. For this reason it took a long period of time to transfer thermal energy to the molecules in the probe. The water had particles of matter that were closer together than the air so, it took a shorter period of time to absorb the heat from the probe.

       The next experiment was to take three different solids (Styrofoam, wood, and metal) and feel the temperature with our hands. The metal felt the coldest, the Styrofoam the warmest, and the wood somewhere in between these estimates. The temperature of each of these solids was measured with the probe. It was strange to find out that their temperatures were all within a few degrees of each other and the room temperature (read from a thermometer). Then the professor told us to think about the fact that all of these materials were in the same temperature environment for a long period of time. This explained why the temperature reading were so similar. This, however, did not tell us why these materials felt so different when held in our hands. This was explained by the arrangement of the molecules in these compounds. The Styrofoam has molecules that are the farthest apart of the three compounds (it is mostly air). This makes it a good insulator because it does not conduct the heat as well as the other two materials. Metal has a large number (sea) of free electrons; it is considered a good conductor of heat. It felt cold to us because it was faster at pulling the thermal energy from our hands than the other materials. The wood block has about the same number of molecules as the metal rod, but no free electrons. This material was therefore able to conduct heat from our hands but, more slowly than the metal. The temperature fluctuations read from the temperature probe for the metal, Styrofoam, and wood (24 C, 19.5 C, and 20.5 C respectively) can also be explained by the statement above. We had held the materials in our hands for different periods of time thereby transferring an unknown amount of thermal energy from our hands to the solids.
     Next, two experiments were done to assess the change in thermal energy when a certain quantity of hot and cold water were mixed together. The first experiment involved two equal amounts (100 mL) of hot (76 C) and cold (13 C) water. The final temperature of the combined water was predicted to be an average of the two temperatures (44 C) before the test. The actual temperature was measured to be 41 C, fairly close to our prediction. The next experiment was very similar to the one above with the exception of the amount of water used. Cold water (50 mL) and hot water (100 mL) were combined and the resulting temperature was above room temperature, what the group had predicted.

Heat Pulsar Setup Diagram

    The final experiment was done with groups of at least four people each. A heat pulsar (see illustration above) was used to deliver a measured number of heat pulses to the water in an insulted cup. Before beginning the heat pulses, the Styrofoam cup was massed and water (172.8 g) added. A graph was plotted of the temperature vs. the pulse energy output (joules/coulomb). The computer froze while trying to save the file, so this group estimated the curve using the initial and final joule measurements (last graph below). The calculated energy required to raise the temperature of the water one degree Celsius was 4335 kJ/kg C. This value is known as the specific heat of water. The formula for calculating the specific heat is: (Joules)/(Grams * Celsius).

                                                                                                                                                     (Thanks to: 3 Ton's of Beast! ))

   The experiments done last week focused on some of the concepts surrounding kinetic theory. A better understanding was reached for the way in which molecules of the same substance and different substances are able to transmit thermal energy to each other. A relationship was discovered between materials that make good conductors and their number of free electrons. The specific heat of a substance was both defined and calculated during this lab.

(Background image of the sun using an extreme ultraviolet imaging telescope thanks to NASA).

Newtonian Physics/ Transitors ~ This is my web page from last year. It has some history
                                                about Sir Isaac Newton and his theories. It also has some nice
                                                links to the history of transistors and a paper on how they
                                                work.

Bragg Diffraction ~ This page was created by my friend and co-worker Sky. In this page she
                             discusses the concepts of Bragg diffraction or the diffraction of x-rays
                             through the use of single crystal diffraction gratings. It also shares great
                             historical information about the discovery of x-rays.

Diffraction ~ This page was created by another friend, Joel. He has some nice graphics of
                    diffraction. The information here talks more about the concepts of diffraction
                    using a laser and a regulator diffraction grating (similar to a hologram).

Spectra analysis using Diffraction ~ This page was created by Charla, a good friend and
                                                    martial arts buddy of mine. It contains a great tiled
                                                    background of the spectra seen through a diffraction
                                                    grating transposed onto a scale or meter stick. It discusses
                                                    how the wavelengths of light emitted by a diffusion tube
                                                    (often misnamed as neon lights) can be calculated through
                                                    the use of a laser and diffraction grating.

Photoelectric Effect ~ This Page was created by a great guy, Chilumba. His webpage focuses
                                 on to use of a phototube (or vacuum tube) that takes in photons or light
                                to produce a usable current for electricity. Vacuum tubes were the
                                 predecessors of transistors. Color filters were used to find the effect of
                                 the different wavelengths of light on the phototube.