1. Physics 101: Lecture 27, Pg 1 Physics 101: Lecture 27 Specific Heat and Latent Heat l Today’s lecture will cover Textbook Sections 12.6 - 12.8

2. Physics 101: Lecture 27, Pg 2 How To Change the Temperature of a System (Solids or Liquids): l Add or subtract heat è Q = heat = energy that flows from warmer to cooler systems. l Q = c m  T è 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 n 1 cal = 4.186 J n 1 kcal = 1 Cal = 4186 J è c = specific heat capacity: Heat required to raise 1 kg by 1 o C. l Q = c m  T : “Cause” = “inertia” x “effect” (just like F=ma) è cause = Q è effect =  T è inertia = c m (mass x specific heat capacity) l  T = Q/(cm) (just like a = F/m)

3. Physics 101: Lecture 27, Pg 3 Examples of Specific Heat Capacity (see Text, Table 12.2) Substance c in J/(kg C) Aluminum900 Copper387 Iron452 Lead128 Water (15 C)4186 Ice (-15 C) 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 c) the same correct Q= c m  T

4. Physics 101: Lecture 27, Pg 4 Latent Heat T Q added to water water temp rises 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 L f (J/kg) L v (J/kg) water33.5 x 10 4 22.6 x 10 5 water changes to steam (boils) steam temp rises 100 o C

5. Physics 101: Lecture 27, Pg 5 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.