PHYS320 ilab (O) Experiment 2 Instructions Conservation of Energy: The Electrical Equivalent of Heat

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PHYS320 ilab (O) Experiment 2 Instructions Conservation of Energy: The Electrical Equivalent of Heat Objective: The purpose of this activity is to determine whether the energy dissipated by a heating

1 PHYS320 ilab (O) Experiment 2 Instructions Conservation of Energy: The Electrical Equivalent of Heat Objective: The purpose of this activity is to determine whether the energy dissipated by a heating resistor in water is equal to the energy absorbed by the water. You will use a Temperature Sensor to measure the change in temperature of a known quantity of water while a heating resistor warms the water using a measured amount of electric energy. You will use DataStudio to record and display the data. You will compare the measured electrical equivalent of heat to the accepted value. Parts and Equipment Required: Computer with PASCO DataStudio software installed PASCO PasPort USB link PASCO PasPort temperature sensor DataStudio experiment files: PHYS320_W2_lab2O_e.ds, PHYS320_W2_lab2O_c.ds Digital Multimeter (DMM) Hand Generator DC power supply or 6V lantern battery (optional) One pair banana-alligator clip leads 10 Ohm 1 Watt Resistor Two pieces of hook-up wire approximately 12 inches long (optional) electrical tape heat shrink tubing (optional) 3 styrofoam beverage cups (8 ounce minimum), lid optional Beaker or measuring cup marked in millilitres Water Steel bolt String Introduction: When water is heated by submerging a heating resistor in the water and running a current through the resistor, the Joule heat from the resistor is transferred to the water and causes the temperature to change. Using conservation of energy, if there are no energy losses to the surroundings, all the energy given off by the resistor should be absorbed by the water. The energy, E, dissipated by the resistor is E = Pt where t is the time during which the current flows through the resistor and P is the power given by P = V 2 R where R is the measured value of the resistance and V is the voltage PHYS320 ilab (O) Instructions Page 1 Experiment 2

The electrical equivalent of heat is the number of joules of electrical energy that are equivalent to one calorie of thermal energy. Procedure: I. Set-up 1.

Bend one of the wire leads so that it touches the body of the resistor and secure it with a small piece of electrical tape so that the leads both point in the same direction and the

Figure 1 10 ohm 1 watt resistor Figure 2 Resistor with electrical tape The final result should look like the resistor in Figure 3. Figure 3 Completed heating resistor 2.

2 across the resistor. The energy gained by the water is given by Q = mc T where m is the mass of the water, c is the specific heat of water (1 cal/g C), and T is the change in temperature of the water. The electrical equivalent of heat is the number of joules of electrical energy that are equivalent to one calorie of thermal energy. Procedure: I. Set-up 1. Prepare the heating resistor (Figure 1) by wrapping a small piece of electrical tape around the body of the resistor, tightly twisting the tape around the lead as shown in Figure 2. Bend one of the wire leads so that it touches the body of the resistor and secure it with a small piece of electrical tape so that the leads both point in the same direction and the resistor forms a compact unit that will fit in the styrofoam cup. Figure 1 10 ohm 1 watt resistor Figure 2 Resistor with electrical tape The final result should look like the resistor in Figure 3. Figure 3 Completed heating resistor 2. (Optional) If you are comfortable soldering, prepare the heating resistor by soldering a 12-inch length of hook-up wire to each lead of the resistor. Use heatshrink tubing or electrical tape to insulate the connections and twist the leads to form a compact unit that will fit in the styrofoam cup. Figure 4 Optional heating resistor The final result should look like Figure Measure the resistance with a DMM and record the measured value on your data sheet. PHYS320 ilab (O) Instructions Page 2 Experiment 2

3 4. Check that the hand-crank generator is working by turning the handle. The light bulb should glow. Be careful not to break the handle. Unscrew and remove the light bulb and attach the plug with the wire leads. 5. Connect the generator to the resistor by clipping the red lead to one wire and the black lead to the other. 6. Connect the digital multimeter to the resistor by connecting the red and black leads to the same wires as the generator. Connecting red to red and black to black. 7. Turn the DMM on and set it to measure DC volts on the 20 V scale. 8. Turn the handle on the generator and check that a voltage is generated. 9. Practice turning the generator until you can produce a relatively steady voltage of 4 volts. 10. (Optional) Use the banana-alligator leads to connect the heating resistor to the DC power supply. Set the voltage to 6.00 volts. Check the voltage with a DMM. Record the voltage on the data sheet. Disconnect the leads but leave the power supply on. If a power supply is not available, you can connect the heating resistor to a 6-volt lantern battery. 11. Connect the Temperature Sensor to the PASCO Pasport Interface and connect the interface to the computer. 12. Download the DataStudio activity file PHYS320_W2_lab2O_e.ds from Doc Sharing and start DataStudio. 13. Open the DataStudio file: PHYS320_W2_lab2O_e.ds. 14. The DataStudio file has one Graph: Temperature-time and one display Current Temperature. Data recording is set at 1 Hz for the temperature. Recording stops automatically after 5 minutes have passed. II. Part 1: Data Collection 1. Press the start button and record room temperature for one run to get a baseline. 2. Nest the two styrofoam cups to double the insulation. Use a measuring cup to carefully measure out 100 ml of cool tap water. Pour the water into the nested styrofoam cups. Using the conversion factor that 1 ml of water has a mass of 1 gram, record the mass of the water on the data sheet. NOTE: Use water that is about one to two degrees Celsius below room temperature when data collection begins. Take data until the temperature of the water is above room temperature or until 5 minutes have elapsed. This minimizes the effect of the surroundings because the water gains energy from its surroundings for half the activity and loses energy to its surroundings for the other half of the activity. 3. If you have a lid that will fit over the top of the cup, make one hole in the lid for the Temperature Sensor, and a second hole in the lid for the heating resistor. 4. Put the heating resistor through its hole in the lid. Submerge the resistor in the water. CAUTION! Be sure the resistor is submerged in water when the current is flowing through it. Otherwise, it can burn up! 5. Put the Temperature Sensor through its hole in the lid of the cup. 6. The experiment should look similar to Figure 5. PHYS320 ilab (O) Instructions Page 3 Experiment 2

Figure 5 Set-up for Lab #2 7. Start recording data a second time without power applied to the resistor to get a baseline for the water temperature. 8. Start recording data a third time.

4 Figure 5 Set-up for Lab #2 7. Start recording data a second time without power applied to the resistor to get a baseline for the water temperature. 8. Start recording data a third time. Start turning the handle on the generator maintaining a voltage of approximately 4 V or connect the heating resistor to the power supply. 9. Keep generating a steady voltage for 4 minutes. When the time reaches 4 minutes, or 240 seconds, stop turning the generator, but stir the water with the temperature sensor and continue to collect data for the full 300 seconds. The temperature will continue to rise as the last bit of thermal energy from the resistor is slowly given off. If you can find someone to help you with your lab, you should have your assistant stir the water during the entire experiment. 10. Your final graph will look similar to the one shown in Figure 6. Figure 6 Sample data 11. Paste a copy of your final graph on your data sheet. PHYS320 ilab (O) Instructions Page 4 Experiment 2

III. Part 1: Analysis 1. Use the graph to find the initial and final temperature of the water. 2. Click Scale to Fit to rescale the graph if needed. 3. Click the Temperature plot to make it active.

5 III. Part 1: Analysis 1. Use the graph to find the initial and final temperature of the water. 2. Click Scale to Fit to rescale the graph if needed. 3. Click the Temperature plot to make it active. Click the smart tool to find an initial time and temperature and a final time and temperature as shown in Figure 7. Record these data on your data sheet. Figure 7 Using the smart cursor to find the initial temperature 4. Calculate (in calories) the thermal energy (Q) absorbed by the water using Q = mc T, where m is the mass of the water, c is the specific heat of water (1cal/g C), and T is the change in temperature of the water. Record this value in the Data Table. 5. Calculate (in joules) the electrical energy (E) output by the generator using E = V2 t where V is R the average voltage, R is the resistance of the heater, and t is the amount of time in seconds that the energy was supplied. 6. By the law of conservation of energy, the electrical energy used by the resistor should equal the thermal energy gained by the water, neglecting losses to the surroundings. 7. Solve for the number of joules per calorie: i. E. E. H. J Electrical Energy = cal Thermal Energy 8. Calculate the percent difference between this experimental value and the accepted value (4.186 J/cal). Record the percent difference in the Data Table. IV. Part 2: Set-up 1. Download the DataStudio activity file PHYS320_W2_lab2O_c.ds from Doc Sharing and start DataStudio. 2. Open the DataStudio file: PHYS320_W2_lab2O_c.ds. 3. The DataStudio file has one Graph: Temperature-time and one display Current Temperature. Data recording is set at 1 Hz for the temperature. Recording stops automatically after two minutes have passed. PHYS320 ilab (O) Instructions Page 5 Experiment 2

6 4. Tie the string to the bolt with about 6 8 inches hanging off. You will use this to transfer the bolt from one cup to another. 5. Fill one styrofoam cup with 50 ml of water, and set it inside a second cup (this is for added insulation). 6. Place the lid on the cup, and allow it to reach room temperature. 7. Bring water to a boil (using either the stove or microwave) and transfer about 200 ml to the remaining cup. The exact amount of hot water is not critical. V. Part 2: Data Collection 1. Place the bolt and temperature sensor into the hot water, and press the start button in DataStudio to record the temperature of the hot water for one run. 2. After the first run is complete, remove the temperature sensor from the hot water, wipe it dry, and place it in the room temperature water in the calorimeter cup. 3. Start recording data a second time to measure the temperature of the water in the calorimeter cup. 4. After 1 minute, transfer the hot object into the calorimeter cup. 5. Use the temperature sensor to stir the water in the cup. Record the highest temperature the thermometer reads over the course of a minute or two. This is the temperature at which the bolt and water reach thermal equilibrium. 6. Record all temperature values in the table on your datasheet. The initial temperature of the bolt is the same as the temperature of the hot water at the end of the first data run. The initial temperature of the water is the temperature just before you placed the bolt in the room temperature water. 7. Use your results to answer the questions and complete the data sheet. 8. Turn in your completed data sheet into your instructor. PHYS320 ilab (O) Instructions Page 6 Experiment 2

EXPERIMENT 14 SPECIFIC HEAT OF WATER. q = m s T

EXPERIMENT 14 SPECIFIC HEAT OF WATER INTRODUCTION: Heat is a form of energy which can pass from an object of relatively high temperature to an object of relatively low temperature. One physical property