Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Purpose Understand how the total energy in a closed system is conserved during heat exchange. Learn how to determine specific heat capacities of certain materials.

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature The Heat Capacity of an Object Amount of heat (energy) that needs to be added to the object in order to raise its temperature by 1 degree Kelvin. Heat added (in Joules) Heat capacity (in Joules/Kelvin) Change in Temperature (in Kelvin) If Q > 0 then T final > T initial (temperature rises) If Q < 0 then T final < T initial (temperature drops)

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature The heat capacity depends on:  Type of Material  Amount of the material (more water has more heat capacity……… you need more energy to raise its temperature……… The specific heat capacity is defined as and has units of or The specific heat capacity only depends on the material, not on the amount of the material.

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature The Specific Heat Capacity Amount of heat (energy) per unit mass that needs to be added to a material in order to raise its temperature by 1 degree Kelvin. Heat added (in Joules) Specific Heat capacity Change in Temperature (in Kelvin) mass of the object

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Example and Implications of Specific Heat Capacity A calorie is defined as the amount of heat that needs to be added to 1 gram of water in order to raise its temperature by 1 degree Kelvin. Water has a relatively high heat capacity, which is important in biology and engineering:  Prevents your body (= mostly water) from heating up too quickly during exercise (an apple that contains 60Kcal of energy has the potential to raise the temperature of a 60Kg person by only  T = Q/(c*m) = 60000cal/(1 cal g -1 K –1 * 60000g)=1Kelvin (assuming all the energy in the apple would go to heat and none to work performed)  Is a good coolant for engines (can absorb a lot of heat without having its temperature rise a lot.

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Heat Transfer Between Two Objects (assume no heat is lost to the environment) m 1 c 1 T 1, initial T 2, initial m 2 c 2 Before contact: After reaching thermal equilibrium they both have the same temperature m 1 c 1 T 1, final T 2, final m 2 c 2 T 1, final = T 2, final = T final Given: m 1, m 2, c 1, c 2, T 1,initial, T 2,initial (T final unkown)

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Because no heat is lost to (or gained from) the environment: The originally colder object gains energy (a positive Q) The originally hotter object looses energy (a negative Q)  Solve for T final

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Activity 1: Calibration of Temperature Probe Themocouples are very easily built temperature sensors. Two dissimilar conductors touching each other produce a voltage V that changes with temperature T. Over certain temperature ranges T is proportional to V and one can calibrate them by finding the voltage for two temperature points and then making a linear approximation. Thermocouple voltages can then be related to temperature. V T T cold V cold V hot T hot Two calibration points

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Activity 1: Calibration of Temperature Probe Alcohol thermometer (read off temperature here) Temp. Probe 750 Interface Use ice bath and warm water bath for the two calibration points

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Activity 2: Determining the Power Output of the Heater Temp. Probe 750 Interface Styrofoam cup filled with 150 ml water. Make sure heater doesn’t touch styrofoam !!!!! Computer: Capstone Switches Heater on/off Heater Switch Box Red LED: Heater is ON Make sure this is plugged in the right way (ground to ground); ground is marked on tape Stand + clamp heater

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Observe total temperature change  T due to heating: time Temperature Heater on Turn Heater off (Turn off “Signal Generator” in Capstone) TT tt After switching heater off. First part with heater on Activity 2: Determining the Power Output of the Heater

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Activity 2: Determining the Power Output of the Heater Click here to open signal generator panel First click on “Auto” : This ensures that when you hit “Record” the heater automatically starts with the recording. Click on “Record” (lower left corner of Capstone). After a fixed (known) amount of time stop just the heater (but not temperature measurement) by clicking “OFF”. To stop temperature recording, click on the “Stop” button in the lower right corner.

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Power = Energy / time = c m  T /  t Compare your result to the power rating written on the heating element. This is the heat/energy given off to the water ( = “Q” ) Activity 2: Determining the Power Output of the Heater

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Activity 3: Determine Specific Heat Capacity of Isopropyl Alcohol Design an experiment to measure c isopropyl alcohol Use your measured power rating of the heating element. DO NOT DRAIN THE ISOPROPYL ALCOHOL INTO THE SINK !!!!! It is illegal to do that and we also do not want to waste the alcohol – it costs money. Instead, please pour it back into the container from which you got it. Caution: Isopropyl alcohol is a flammable liquid. If you accidentally spill it over a power outlet, do not unplug the equipment. Sparks may ignite the alcohol!

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Activity 4: The Transfer of Heat Caution: This experiment uses liquid nitrogen, which is extremely cold. Follow the safety instructions! Liquid nitrogen (LN2) Water at Room Temperature Brass disc on a string Step 1: Cool brass in the LN2 (wait until bubbling stops) Step 2: Put cold brass (-197ºC) into water. Step 3: Monitor temperature

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Step 4: Determine the specific heat capacity of brass Step 5: Compare your value of c brass to that in the literature (you can surely find that value on the internet) Activity 4: The Transfer of Heat

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Hints Do not be surprised if the power rating of the heater element disagrees with what you measured. When we measured the resistance of the heating elements with wires, some were as high as 2 Ohms. Therefore, a more realistic power rating may be about …and it may be even lower if the supplied voltage is less than 12 Volts (on some of the heater boxes)  That’s why you need to use your measured power rating in Activity 3, not the official rating.

Physics 1809 Minilab 2: Heat and Temperature Physics 1809: The Relationship Between Heat and Temperature Liquid Nitrogen Safety Wear goggles when using liquid nitrogen. Pour liquid nitrogen slowly and very carefully. Do not deliberately spill liquid nitrogen. When putting the brass object into liquid nitrogen, suspend it on a string and carefully lower it into the liquid nitrogen (the nitrogen will boil rapidly). Do not touch liquid nitrogen or metal surfaces that are in direct contact with liquid nitrogen. Never put liquid nitrogen into a closed container (except into specially designed containers with pressure relief and safety valves). It will explode and you may be seriously injured or killed by the exploding fragments. When carrying liquid nitrogen to your table, walk carefully and make sure nobody bumps into you (or you into them). When done with your liquid nitrogen, you can carefully pour it back into the dewar.