lecture35 - II. Heat 1. Heat and energy A little bit of...

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II. Heat 1. Heat and energy Calorie: the amount of heat required to raise the temperature of 1 gram of water from 14.5 C to 15.5 C. A little bit of history: Old theories Robert von Mayer (1814-1878) James Joule (1818-1889) Hermann von Helmholtz (1821-1894) 1 cal = 4.186 J
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2. Specific heat dT dQ m c 1 K kg J C g cal c water 4190 1 1 cal = 4.186 J cmdT dQ T cm Q 2a. Heat capacity dT dQ C CdT dQ T C Q cm C
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2b. Calorimetry Δ Q=cm Δ T 0 i Q Example: 200 g of water at the temperature of 80°C is placed into a 50 g glass at 20°C. What is the final temperature of the system. m w = 200 g T w = 80º C c w =1.0 cal/g m g = 50 g T g = 20º C c g = 0.20 cal/g T=T f -? 0 g w Q Q 0 ) ( w w w w T T m c Q 0 ) ( g g g g T T m c Q 0 ) ( ) ( g g g w w w T T m c T T m c g g w w g g g w w w m c m c T m c T m c T 0 i Q 0 ) ( i i i T T m c i i i i i m c T m c T C T 77
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Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change? 1) the one with the higher initial temperature 2) the one with the lower initial temperature 3) the one with the greater mass 4) the one with the smaller mass 5) the one with the higher specific heat Since the objects are made of the same material, the only difference between them is their mass. Clearly, the object with less mass will be much easier to change temperature since there is not much material there (compared to the more massive object). A
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lecture35 - II. Heat 1. Heat and energy A little bit of...

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