Physics 101 Lecture 27 Specific Heat and Latent Heat Today s lecture will cover Textbook Sections 12 6 12 8 Physics 101 Lecture 27 Pg 1 How To Change the Temperature of a System Solids or Liquids Add or subtract heat Q heat energy that flows from warmer to cooler systems Q c m T Q amount of heat that must be supplied or subtracted to raise or lower the temperature of mass m by an amount T Units of Q Joules or calories 1 cal 4 186 J 1 kcal 1 Cal 4186 J c specific heat capacity Heat required to raise 1 kg by 1oC Q c m T Cause inertia x effect just like F ma cause Q effect T inertia c m mass x specific heat capacity T Q cm just like a F m Physics 101 Lecture 27 Pg 2 Examples of Specific Heat Capacity see Text Table 12 2 Q c m T Substance Aluminum Copper Iron Lead Water 15 C Ice 15 C c in J kg C 900 387 452 128 4186 2000 Suppose you have equal masses of aluminum and copper at the same initial temperature You add 1000 J of heat to each of them Which one ends up at the higher final temperature a aluminum b copper correct c the same Physics 101 Lecture 27 Pg 3 Latent Heat T 100oC water temp rises water changes to steam boils steam temp rises Q added to water Q m L with L Latent Heat L J kg Q is the amount of heat needed to add or remove from a substance with mass m to change the state of that substance Liquid Solid fusion energy Liquid Gas vaporization energy Solid Gas sublimation energy Substance Lf J kg Lv J kg water 33 5 x 104 22 6 x 105 Physics 101 Lecture 27 Pg 4 Concept Question Summers in Phoenix Arizona are very hot 125 F is not uncommon and very dry If you hop into an outdoor swimming pool on a summer day in Phoenix you will probably find that the water is too warm to be very refreshing However when you get out of the pool and let the sun dry you off you find that you are quite cold for a few minutes How can you explain this The water is evaporating off of your skin This means that enough heat or energy is entering the water drops to break bonds between water and allow them to evaporate Where is this heat coming from Your body Heat flows from your body to the drops of water making you feel cooler When the water is gone no more heat will flow from your body and you will get hot once again Physics 101 Lecture 27 Pg 5
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