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PHYS320 iLab (O) Experiment 2 Conservation of Energy: The Electrical Equivalent of Heat DATA SHEET Name: __________________ Date: ___________ 6...

Physics 320 Week 2 lab, Conservation of Energy: The Electrical Equivalent of Heat

PHYS320 iLab (O) Experiment 2 Conservation of Energy: The Electrical Equivalent of Heat DATA SHEET Name: __________________ Date: ___________ 6 questions @ 1 point each; 4 questions @ 2 points each; and 4 questions @ 4 points each. 30 points total. Part 1 1. The measured resistance of the heater is (1 point) 2. The voltage applied across the heating resistor is V (1 point) 3. The power dissipated by the heating resistor is W (1 point) 4. The mass of water in cup is grams (1 point) 5. Paste a copy of your temperature–time graph here. (1 point) 6. Data Table (4 points) Item Amount Item Amount initial time t i s initial temperature T i ˚C final time t f s final temperature T f ˚C change in time s Change in Temp. ˚C Item Amount Electrical Energy, J Thermal Energy, calories Electrical Equivalent of Heat J/calorie Accepted Value = J/cal Percent difference = ___ ___ ___ % Part 2 7. Paste a copy of the temperature-time graph from Part 2 here. (1 point) 8. Use the data from Part 2 to complete the table below. (4 points) Object Object mass m B (g) Water mass m W (g) Initial water temperature T Wi ( ° C) Initial object temperature T Bi ( ° C) Final temperatur e T f ( ° C) Change in water temperature T W = T f T Wi Change in object temperature T B = T Bi T f Steel Bolt 21.0 PHYS320 iLab (O) Datasheet Page 1 Experiment 2
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9. The heat lost by the hot bolt is equal to the heat gained by the water in the calorimeter. Use the data provided in the table and what you know about heat to solve for the specific heat ( C B ) of the steel. Show your work. (4 points) 10. Look up the specific heat of carbon steel in your text or online. Find the percent difference between your calculated specific heat and the accepted value. Show your work. (4 points) Questions 11. In Part 1, was the thermal energy gained by the water greater, the same as, or less than the electrical energy dissipated by the resistor? Explain. (2 points) 12. The heating resistor is rated at 10 ohms and 1 watt. What percentage of the power rating was used during this activity? Why didn’t the resistor burn up? (2 points) 13. What are some factors that could account for the percent difference between the experimental and the accepted values for the electrical equivalent of heat and for the specific heat of the steel bolt? (2 points) 14. Does the air inside the calorimeter also gain heat? Why do we exclude this from our calculation? (2 points) PHYS320 iLab (O) Datasheet Page 2 Experiment 2
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PHYS320 iLab (O) Experiment 2 Instructions Conservation of Energy: The Electrical Equivalent of Heat PHYS320 iLab (O) Instructions Page 1 Experiment 2 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 ° = ±² where t is the time during which the current flows through the resistor and P is the power given by ± = ³ 2 ´ where R is the measured value of the resistance and V is the voltage
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PHYS320 iLab (O) Instructions Page 2 Experiment 2 across the resistor. The energy gained by the water is given by ° = ±²∆³ 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. The final result should look like the resistor in Figure 3. Figure 1 10 ohm 1 watt resistor Figure 2 Resistor with electrical tape 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 heat- shrink tubing or electrical tape to insulate the connections and twist the leads to form a compact unit that will fit in the styrofoam cup. The final result should look like Figure 4. Figure 4 Optional heating resistor 3. Measure the resistance with a DMM and record the measured value on your data sheet.
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