1. Physics 2 Chapter 11 Sections 3-4

2. Latent Heat Amount of heat energy per kg that must be added or removed when a substance changes from one phase to another Q = Lm

3. Latent Heat L f = latent heat of fusion = 3.33 x 10 5 J/kg for ice L v = 2.26 x 10 6 J/kg for water Table of values p 375

4. Sample Problem A 7 kg glass bowl (c=840 J/kgC⁰) contains 16 kg of punch at 25 ⁰C. 2.5 kg of ice (c=2000 J/kgC⁰) are added to the punch. The ice has an initial temperature of -20 ⁰C. The punch may be treated as if it were water (c=4186 J/kgC⁰). What is the temperature of the punch, ice, and bowl when they reach thermal equilibrium?

5. Sample Problem How much energy is required to change a 42 g ice cube from ice at -11 ⁰C to steam at 111 ⁰C?

6. Radiation Process by which energy is transferred by means of electromagnetic waves

7. Electromagnetic Wave Wave formed by electric and magnetic fields fluctuating together ex – visible light, radio, microwaves Doesn’t require a medium ex – sunlight travels through vacuum of space

8. Radiation cont’d. All bodies continuously radiate energy in the form of EM waves Objects absorb and emit EM waves simultaneously If object is same temp as surroundings then amt of radiant energy absorbed = amt of radiant energy emitted Material that is a good absorbed is also a good emitter

9. Stefan’s Law Amount of energy emitted by a body depends on time, surface area, temperature P = ΔQ/Δt = σAeT 4 P = rate at which energy is emitted or absorbed σ=Stefan Boltzmann constant e=emissivity – number between 0 and 1 that is characteristic of the material

10. Convection Process in which heat energy is carried from place to place by the bulk movement of fluid When part of a fluid is warmed that part expands, decreasing density, causing it to rise -----cooler fluid replaces it ----- repeats

11. Convection Rate of heating can be approximated by H = hAΔT H= rate of convection heating h=convection coefficient A= surface area of body ΔT= temperature difference

12. Conduction Process where heat energy is transferred directly through a material Bulk motion of the material plays no role in transfer Energy is transferred when atoms in hotter part collide and pass on energy to atoms in cooler part Metals are good conductors due to free electrons

13. Conduction ΔQ/Δt = kAΔT/d k= thermal conductivity – depends on type of material