Physics 101: Lecture 27 Specific Heat and Latent HeatHow To Change the Temperature of a System (Solids or Liquids):Examples of Specific Heat Capacity (see Text, Table 12.2)Latent HeatConcept QuestionPhysics 101: Lecture 27, Pg 1Physics 101: Physics 101: Lecture 27Lecture 27Specific Heat and Latent HeatSpecific Heat and Latent HeatToday’s lecture will cover Textbook Sections 12.6 - 12.8Physics 101: Lecture 27, Pg 2How To Change the Temperature of a How To Change the Temperature of a System (Solids or Liquids):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 3Examples of Specific Heat CapacityExamples of Specific Heat Capacity(see Text, Table 12.2)(see Text, Table 12.2)Substance c in J/(kg C)Aluminum 900Copper 387Iron 452Lead 128Water (15 C) 4186Ice (-15 C) 2000Suppose 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 temperaturea) aluminumb) copperc) the samecorrectQ= c m TPhysics 101: Lecture 27, Pg 4Latent HeatLatent HeatTQ added to waterwater temp risesQ = m L with L = Latent Heat L [J/kg]:Q is the amount of heat needed to add or remove from a substancewith 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 105water changesto steam(boils)steam temp rises100oCPhysics 101: Lecture 27, Pg 5Concept QuestionConcept QuestionSummers 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
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