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Heat Capacity

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Work In The work - energy principle applies to all objects. If an object speeds up it gains kinetic energy. If an object slows down it loses kinetic energy. Work done on a system v2v2 v1v1

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Heat In Temperature change is due to heat (Q). If an objects temperature increases it gains heat. If an objects temperature decreases it loses heat. Heat into a system

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Heat Capacity The ratio of the change in heat to the change in temperature is the heat capacity (C). The ratio of the change in heat to the change in temperature is the heat capacity (C). Depends on materialDepends on material Depends on the massDepends on the mass Measured in J/KMeasured in J/K

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Specific Heat The ratio of the change in heat to the change in temperature is the heat capacity (C). The ratio of the change in heat to the change in temperature is the heat capacity (C). Depends on materialDepends on material independent of the massindependent of the mass Measured in J/kg-KMeasured in J/kg-K MaterialSpecific heat Mercury140 J/kg-K Copper390 J/kg-K Steel500 J/kg-K Granite840 J/kg-K Aluminum900 J/kg-K Wood1400 J/kg-K Ice2100 J/kg-K Water4200 J/kg-K

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Take a Shower You are last to use the shower today and the temperature in the water heater has dropped to 18 C from the normal temperature of 50 C. The heater holds 150 kg and has a 50 kW heating coil. You are last to use the shower today and the temperature in the water heater has dropped to 18 C from the normal temperature of 50 C. The heater holds 150 kg and has a 50 kW heating coil. How long should you wait before starting your shower? How long should you wait before starting your shower? Find the heat required. Q = mc T = (150 kg) (4200 J/kg-K) ( 32 C) Q = 2.1 x 10 7 J Find the time from the power, and set the heat to the work. P = W/ t t = Q / P (2.1 x 10 7 J) / (5 x 10 4 W) t = 4000 s = 1.1 hr

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Equilibrium Temperature Two systems in thermal contact will adjust to reach the same temperature - thermal equilibrium Two systems in thermal contact will adjust to reach the same temperature - thermal equilibrium If they are thermally insulated, all the heat goes from the hot system to the cold system. If they are thermally insulated, all the heat goes from the hot system to the cold system. 12

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Doing Dishes A 1.5 kg aluminum pan is heated to 180 C then placed into a sink with 8 kg water at 20 C. A 1.5 kg aluminum pan is heated to 180 C then placed into a sink with 8 kg water at 20 C. If no water boils, what is the equilibrium temperature? If no water boils, what is the equilibrium temperature? Setup the equation for an unknown equilibrium temperature T. Solve for T. T = 26 C next

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