PHYS 1405 Conceptual Physics I Heat and Temperature

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1 PHYS 1405 Conceptual Physics I Heat and Temperature Materials Laptop LabPro Heat Pulser Immersion Heater Stainless temperature probe Styrofoam cup, large Styrofoam cup, small Introduction In this activity we will explore the relationship between heat and temperature. Our procedure will be to add heat to a beaker of water in known equal increments and measure the effect on the temperature of the water. Safety In this activity we will make use of immersion heaters. Immersion heaters must be immersed in water before they are plugged in. If you plug them in without first immersing them, they will glow red hot and possibly melt, presenting a considerable risk of burning you and also of possibly starting a fire. Be sure to have the immersion heater plugged in only during the indicated times during the procedure. Also, always make sure that the immersion heater is not immersed beyond the bottom of the plastic handle. (You want it in the water but not too much!) Procedure SMALL CUP Q1. Use the electronic balance to determine the mass of the small styrofoam cup. Fill the cup with about 100 ml of water and record the mass again. Determine the mass of the water in the cup. mass of Styrofoam cup mass of Styrofoam cup + water mass of water grams kilograms Set-up Do not plug in the immersion heater until instructed to do so. Place the coil of the immersion heater into the water. Water should not go above the plastic handle on the immersion heater. Make sure that the LabPro has power and is connected to the laptop using one of the USB ports in the back of the laptop. Plug the heat pulser into DIG/SONIC 1 on the LabPro and connect the stainless temperature probe into CH 1 on the LabPro. Plug the 120 V cord connected to the heat pulser into an outlet. Open LoggerPro 3 and click on the open icon and open the experiment file by following the path Probes & Sensors=> Heat Pulser=>Heat Pulser 5s. 21-heat and temperature 01.doc - 1 -

2 In this experiment file, in addition to the normal Collect button, you will also have a button that reads Pulse. Each time you click on the pulse button, it will turn the heater on for 5 s. Verify that the immersion heater is immersed correctly into the water and then plug the immersion heater into the outlet on the heat pulser. Click on the Collect button and LoggerPro will start to record the temperature of the water. Use the stainless steel temperature probe to stir the water continually during this measurement procedure. (1.) Measure the initial temperature of the water until it reaches a steady value, and then click on the Pulse button one time. The heater will turn on for 5 s. (2.) Observe the temperature. It should go up for 5 s or so and then maintain a steady value. (3.) Once the temperature has reached a steady value, click on the pulse button again. Keep repeating this procedure for 10 pulses or until the experiment stops. Remember to continually stir the water. Unplug the immersion heater at this point. Recording the Data Click on the Examine button. When it is selected, as you scroll over the data, a box will appear which gives you the Temperature and time for each data point. Record the initial temperature of the water before the first pulse was clicked. Record it in the data table below in the row for step 0. Move the cursor to a data point where the temperature has reached a steady value after the first pulse ended. Record the value of the temperature in the row for step 1. Repeat until you have obtained the temperature after each pulse. Step # Temperature (C ) T In the table above, record the change in temperature after each input of heat. For instance T 1 = T 1 T 0, T 2 = T 2 T 1, etc 21-heat and temperature 01.doc - 2 -

3 Data Analysis Q2. When you clicked on the Pulse button the heater turned on for 5 s. If the power rating of the heater is 120 W, how much energy was given off by the heater? Q3. Where did that energy go? Q4. Heat is defined as a flow of energy form a hotter object to a cooler one. Assuming no losses to the beaker or the air, how much heat was added to the water during each pulse? Q5. Was the temperature change roughly constant for each pulse of heat added? Q6. Did a constant amount of heat input produce a constant temperature change? Q7. How is the amount of heat added related to the change in temperature? Q8. If instead of adding heat, we removed heat. What would be the effect on the temperature? Procedure LARGE CUP Determine the mass of the large Styrofoam cup and then fill it with 200 ml of water. Q9. Determine the mass of the water in the cup. mass of Styrofoam cup mass of Styrofoam cup + water mass of water grams kilograms Set Up Verify that the immersion heater is immersed correctly into the water and then plug the immersion heater into the outlet on the heat pulser. Repeat the procedure and data collection that you conducted previously for the Larger cup with a greater amount of water. Record your temperature readings in the table below. 21-heat and temperature 01.doc - 3 -

4 Step Temperature (C ) T In the table below, record the change in temperature after each input of heat. For instance T 1 = T 1 T 0, T 2 = T 2 T 1, etc Data Analysis Q10. Was the temperature change still roughly constant for each input of heat? Q11. How did the size of the temperature change compare when you had twice as much water compare to the size of the previous temperature change. Q12. When you had twice the volume of water, how much more mass of water did you have in the cup? Q13. What type of relationship do your answers to Q11 and Q12 suggest exists between the change in temperature and the mass? Specific Heat Calculation We have seen that the temperature went up a roughly a constant amount each time a pulse of heat was added. Further, the amount the temperature went up was less for more mass and greater for less mass. We can combine these observations into a single formula relating heat mass and temperature change. Heat = constant x mass x Change in temperature. It is customary to use the letter Q to denote the heat, so in symbols the formula becomes Q = c m T. The constant is known as the specific heat and is a property of the material that you are studying. From our data, we can determine the specific heat for water. We will do so for each set of data. Q14. From your first data set (Small Cup) determine the total T from the time before the first pulse was added to the time after the last pulse was added. T = 21-heat and temperature 01.doc - 4 -

5 Q15. You added 600 J of heat in each pulse, so what was the total amount of heat added from all of the pulses? Enter this number in the table below. Q16. What was the mass of the water used in the first data set in kg? Enter it in the table below Q17. Plug in your values into the formula Q = c m T and solve for the specific heat of water. Include units. Q18. Repeat you calculation of the specific heat for the second set of data. Small Cup Large Cup C Avg % Difference 1 % Difference 2 Q (J) m (kg) T ( C ) C (J/kg- C) = Q/(m T) Q19. Calculate the percentage difference between the Small Cup value and the Large Cup value. Did you obtain values for the specific heat that were close to each other for each set of data? C Avg = (C S + C L )/2 % Difference 1 = (C S - C L ) x 100/ C Avg Q20. Compare C Avg with accepted value. The accepted value of the specific heat of water is 4196 J/(kg C ). Calculate the percentage difference of your C Avg value and the accepted value. % Difference 2 = (C Avg 4196) x 100/ heat and temperature 01.doc - 5 -