1. Review for Test 3 Introduction Section 0 Lecture 1 Slide 1 Lecture 27 Slide 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3

2. Introduction Section 0 Lecture 1 Slide 2 Lecture 27 Slide 2 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 PHYSICS OF TECHNOLOGY Spring 2009 Assignment Sheet *Homework Handout

3. Review for Test 3 Introduction Section 0 Lecture 1 Slide 3 Lecture 27 Slide 3 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Notes on Test 1.Covers Chapters 9-11 2.~8 short answer problems or questions (5 point each) 3.3 Numerical problems based heavily on the material from the homework and Lab/Demo sessions (20 points each). One problem each from Chapters 9, 10 and 11. 4.You will have a formula sheet just like the one in the handout. 5.Test is Thursday March 26 1:30-2:45 in ESLC 46.

4. Review for Test 3 Introduction Section 0 Lecture 1 Slide 4 Lecture 27 Slide 4 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3 Introduction and Review

5. Review for Test 3 Introduction Section 0 Lecture 1 Slide 5 Lecture 27 Slide 5 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 What Do We Need To Measure? What is the minimum about things we need to know? Where things are—a length, L When things are there—a time, t How thing interact with gravity—a mass, M How things interact with E&M—a charge, Q How thing inter act with weak nuclear force How things interact with strong nuclear force Random collections of objects—a temperature, T

6. Review for Test 3 Introduction Section 0 Lecture 1 Slide 6 Lecture 27 Slide 6 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Describing Motion and Interactions Position—where you are in space (L or meter) Velocity—how fast position is changing with time (LT -1 or m/s) Acceleration—how fast velocity is changing with time (LT -2 or m/s 2 ) Force— what is required to change to motion of a body (MLT -2 or kg-m/s 2 or N) Inertia (mass)— a measure of the force needed to change the motion of a body (M) Energy—the potential for an object to do work. (ML 2 T -2 or kg m 2 /s 2 or N-m or J) Work is equal to the force applied times the distance moved. W = F d Kinetic Energy is the energy associated with an object’s motion. KE=½ mv 2 Potential Energy is the energy associated with an objects position. Gravitational potential energy PE gravity =mgh Spring potential energy PE apring = -kx Momentum— the potential of an object to induce motion in another object (MLT -1 or kg-m/s) Angular Momentum and Rotational Energy— the equivalent constants of motion for rotation (MT -1 or kg/s) and (MLT -2 or kg m/s 2 or N)

7. Review for Test 3 Introduction Section 0 Lecture 1 Slide 7 Lecture 27 Slide 7 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Newton’s Laws in Review 1 st Law —a special case of the 2 nd Law for statics, with a=0 or F net =0 An objects velocity remains unchanged, unless a force acts on the object. 2 nd Law (and 1 st Law)—How motion of a object is effected by a force. –The acceleration of an object is directly proportional to the magnitude of the imposed force and inversely proportional to the mass of the object. The acceleration is the same direction as that of the imposed force. 3 rd Law —Forces come from interactions with other objects. For every action (force), there is an equal but opposite reaction (force).

8. Review for Test 3 Introduction Section 0 Lecture 1 Slide 8 Lecture 27 Slide 8 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Energy: The potential to do work. Conservation of Energy: The total energy of a closed system remains constant. –Energy can be converted from one form to another. –Not all forms of energy can be fully recovered. Conservation of Energy Time  Energy 

9. Review for Test 3 Introduction Section 0 Lecture 1 Slide 9 Lecture 27 Slide 9 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Momentum and Impulse Multiply both sides of Newton’s second law by the time interval over which the force acts: The left side of the equation is impulse, the (average) force acting on an object multiplied by the time interval over which the force acts. How a force changes the motion of an object depends on both the size of the force and how long the force acts. The right side of the equation is the change in the momentum of the object. The momentum of the object is the mass of the object times its velocity.

10. Review for Test 3 Introduction Section 0 Lecture 1 Slide 10 Lecture 27 Slide 10 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Impulse-Momentum Principle The impulse acting on an object produces a change in momentum of the object that is equal in both magnitude and direction to the impulse. In analogy, work = change in energy = ΔE

11. Review for Test 3 Introduction Section 0 Lecture 1 Slide 11 Lecture 27 Slide 11 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Formulas We Know and Love Formulas as They Will Appear on the Test Sheet

12. Review for Test 3 Introduction Section 0 Lecture 1 Slide 12 Lecture 27 Slide 12 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3

13. Introduction Section 0 Lecture 1 Slide 13 Lecture 27 Slide 13 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Test 3 Review Concepts Concepts and Terms to Be Familiar With Know what pressure and density are and how this relates to fluids. Know Pascal’s Principle and how to apply it to hydraulics problems. Know how buoyant force is related to pressure and Archimedes’ Principle. Know what an ideal gas is and what the ideal gas law says about pressure volume and temperature of an ideal gas. Understand how conservation of mass is related to flow rate. Understand the difference between laminar and turbulent flow. Understand Bernoulli’s Principle as a fluid form of the conservation of energy. Be able to state the four laws of thermodynamics. Be able to define heat and temperature and explain how they are different. Understand heat capacity, heat of fusion (melting), and heat of vaporization (boiling). Be able to do simple calorimitry problems. Be able to qualitatively explain the difference between the three forms of heat transfer: conduction, convection and radiation. Be able to explain what a heat engine is and what the components of work, high temperature reservoir and low temperature reservoir. What is efficiency of a heat engine? Of a Carnot engine?

14. Review for Test 3 Introduction Section 0 Lecture 1 Slide 14 Lecture 27 Slide 14 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Formulas We Know and Love New Formulas as They Will Appear on the Test Sheet

15. Review for Test 3 Introduction Section 0 Lecture 1 Slide 15 Lecture 27 Slide 15 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3 Fluids and Pressure

16. Review for Test 3 Introduction Section 0 Lecture 1 Slide 16 Lecture 27 Slide 16 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Test 3 Review Concepts Concepts and Terms to Be Familiar With Know what pressure and density are and how this relates to fluids. Know Pascal’s Principle and how to apply it to hydraulics problems. Know how buoyant force is related to pressure and Archimedes’ Principle. Know what an ideal gas is and what the ideal gas law says about pressure volume and temperature of an ideal gas. Understand how conservation of mass is related to flow rate. Understand the difference between laminar and turbulent flow. Understand Bernoulli’s Principle as a fluid form of the conservation of energy. Fluids and Pressure

17. Review for Test 3 Introduction Section 0 Lecture 1 Slide 17 Lecture 27 Slide 17 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 States of Matter

18. Review for Test 3 Introduction Section 0 Lecture 1 Slide 18 Lecture 27 Slide 18 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Pressure The man weighs more, so he exerts a larger force on the ground. The woman weighs less, but the force she exerts on the ground is spread over a much smaller area. Pressure takes into account both force and the area over which the force is applied. –Pressure is the ratio of the force to the area over which it is applied: –Units: 1 N/m 2 = 1 Pa (pascal) –Pressure is the quantity that determines whether the soil will yield.

19. Review for Test 3 Introduction Section 0 Lecture 1 Slide 19 Lecture 27 Slide 19 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Dennison’s Laws of Fluids When push comes to shove, fluids are just like other stuff. Pascal’s Principle: Pressure extends uniformly in all directions in a fluid. Boyle’s Law: Work on a fluid equals PΔV Bernoulli’s Principle: Conservation of energy for fluids

20. Review for Test 3 Introduction Section 0 Lecture 1 Slide 20 Lecture 27 Slide 20 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Pascal’s Principle Fluid pushes outward uniformly in all directions when compressed. Any increase in pressure is transmitted uniformly throughout the fluid. Pressure exerted on a piston extends uniformly throughout the fluid, causing it to push outward with equal force per unit area on the walls and the bottom of the cylinder. This is the basis of Pascal’s Principle: –Any change in the pressure of a fluid is transmitted uniformly in all directions throughout the fluid.

21. Review for Test 3 Introduction Section 0 Lecture 1 Slide 21 Lecture 27 Slide 21 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Pascal’s Principle for Gases Gas molecules lack strong interactions. Pressure is understood as resulting from momentum transfer to the container walls through unbalanced collisions Pressing on one surface adds force and hence imparts impulse to the gas That impulse is taken up as added collisons (pressure) on other surfaces The random nature of the motion of gas particles assures that the force is distributed evenly to all surfaces For fixed walls, a decrease in V results in an increase in P For expandable walls (like a balloon) the volume “appears elsewhere to make up for the lost volume

22. Review for Test 3 Introduction Section 0 Lecture 1 Slide 22 Lecture 27 Slide 22 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Pascal’s Principle for Liquids Liquid molecules have strong interactions. Liquids do not compress much Pressure is understood as resulting from momentum transfer to the container walls through unbalanced spring forces Pressing on one surface adds force that is transferred to other springs The network nature of the forces on the particles assures that the force is distributed evenly to all surfaces For expandable walls (like a balloon) the volume “appears elsewhere to make up for the lost volume For fixed walls, a small decrease in V (a compression) results in a large increase in P For solids, you can think of the strong forces holding the atoms in there equilibrium positions, equivalent to fixed walls + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

23. Review for Test 3 Introduction Section 0 Lecture 1 Slide 23 Lecture 27 Slide 23 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Archimedes’ Principle The average density of an object compared to a fluid determines whether the object will sink or float in that liquid. The upward force that pushes objects back toward the surface in liquids is called the buoyant force. Archimedes’ Principle: The buoyant force acting on an object fully or partially submerged in a fluid is equal to the weight of the fluid displaced by the object.

24. Review for Test 3 Introduction Section 0 Lecture 1 Slide 24 Lecture 27 Slide 24 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Archimedes’ Principle For example, consider a block submerged in water, suspended from a string. –The pressure of the water pushes on the block from all sides. –Because the pressure increases with depth, the pressure at the bottom of the block is greater than at the top. –There is a larger force ( F = PA ) pushing up at the bottom than there is pushing down at the top. –The difference between these two forces is the buoyant force. The buoyant force is proportional to both the height and the cross-sectional area of the block, and thus to its volume. The volume of the fluid displaced is directly related to the weight of the fluid displaced.

25. Review for Test 3 Introduction Section 0 Lecture 1 Slide 25 Lecture 27 Slide 25 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Flow Rate The volume of a portion of water of length L flowing past some point in a pipe is the product of the length times the cross-sectional area A, or LA. The rate at which water moves through the pipe is this volume divided by time: LA / t. Since L / t = v, the rate of flow = vA.

26. Review for Test 3 Introduction Section 0 Lecture 1 Slide 26 Lecture 27 Slide 26 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Laminar flow is smooth flow, with no eddies or other disturbances. –The streamlines are roughly parallel. –The speeds of different layers may vary, but one layer moves smoothly past another. Turbulent flow does have eddies and whorls; the streamlines are no longer parallel. Laminar vs Turbulent Flow

27. Review for Test 3 Introduction Section 0 Lecture 1 Slide 27 Lecture 27 Slide 27 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Bernoulli’s Principle How does a large passenger jet manage to get off the ground? What forces keep it in the air? How is a ball suspended in mid-air by a leaf blower? What happens if we do work on a fluid? Bernoulli’s principle applies conservation of energy to the flow of fluids: The sum of the pressure plus the kinetic energy per unit volume of a flowing fluid must remain constant.

28. Review for Test 3 Introduction Section 0 Lecture 1 Slide 28 Lecture 27 Slide 28 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 How does pressure vary in pipes and hoses? Will the pressure be greatest in the narrow section or the wide section? The speed will be greater in the narrow section. To keep the sum P + 1/2 dv 2 constant, the pressure must be larger where the fluid speed is smaller (h is fixed). If the speed increases, the pressure decreases. (This goes against our intuition.) This can be shown using vertical open pipes as pressure gauges. The height of the column of water is proportional to the pressure. Pressure Changes with Area

29. Review for Test 3 Introduction Section 0 Lecture 1 Slide 29 Lecture 27 Slide 29 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3

30. Introduction Section 0 Lecture 1 Slide 30 Lecture 27 Slide 30 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3 Temperature and Heat

31. Review for Test 3 Introduction Section 0 Lecture 1 Slide 31 Lecture 27 Slide 31 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Test 3 Review Concepts Concepts and Terms to Be Familiar With Be able to state the four laws of thermodynamics. Be able to define heat and temperature and explain how they are different. Understand heat capacity, heat of fusion (melting), and heat of vaporization (boiling). Be able to do simple calorimitry problems. Be able to qualitatively explain the difference between the three forms of heat transfer: conduction, convection and radiation. Temperature and Heat

32. Review for Test 3 Introduction Section 0 Lecture 1 Slide 32 Lecture 27 Slide 32 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Dennison’s Laws Thermal Poker (or How to Get a Hot Hand in Physics) 0 th Law: Full House beats Two Pairs 1 st Law: We’re playing the same game (but with a wild card) 2 nd Law: You can’t win in Vegas. 3 rd Law: In fact, you always loose. 0 th Law: Defines Temperature 1 st Law: Conservation of Energy (with heat) 2 nd Law: You can’t recover all heat losses (or defining entropy) 3 rd Law: You can never get to absolute 0.

33. Review for Test 3 Introduction Section 0 Lecture 1 Slide 33 Lecture 27 Slide 33 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 What is heat? What is the relationship between quantity of heat and temperature? What happens to a body (solid, liquid, gas) when thermal energy is added or removed? Thermal Energy Heat Solid: Atoms vibrating in all directions about their fixed equilibrium (lattice) positions. Atoms constantly colliding with each other. Liquid: Atoms still oscillating and colliding with each other but they are free to move so that the long range order (shape) of body is lost. Gas: No equilibrium position, no oscillations, atoms are free and move in perpetual high-speed “zig-zag” dance punctuated by collisions. gas liquid solid

34. Review for Test 3 Introduction Section 0 Lecture 1 Slide 34 Lecture 27 Slide 34 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 When two objects at different temperatures are placed in contact, heat will flow from the object with the higher temperature to the object with the lower temperature. Heat added increases temperature, and heat removed decreases temperature. Heat and temperature are not the same. Temperature is a quantity that tells us which direction the heat will flow. Heat is a form of energy. (Here comes conservation of energy!!!) Temperature and Heat

35. Review for Test 3 Introduction Section 0 Lecture 1 Slide 35 Lecture 27 Slide 35 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Gas Behavior and The First Law Consider a gas in a cylinder with a movable piston. If the piston is pushed inward by an external force, work is done on the gas, adding energy to the system. The force exerted on the piston by the gas equals the pressure of the gas times the area of the piston: F = PA The work done equals the force exerted by the piston times the distance the piston moves: W = Fd = (PA)d = P  V

36. Review for Test 3 Introduction Section 0 Lecture 1 Slide 36 Lecture 27 Slide 36 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 In an isothermal process, the temperature does not change. –The internal energy must be constant. –The change in internal energy,  U, is zero. –If an amount of heat Q is added to the gas, an equal amount of work W will be done by the gas on its surroundings, from  U = Q - W. In an isobaric process, the pressure of the gas remains constant. –The internal energy increases as the gas is heated, and so does the temperature. –The gas also expands, removing some of the internal energy. –Experiments determined that the pressure, volume, and absolute temperature of an ideal gas are related by the equation of state: PV = NkT where N is the number of molecules and k is Boltzmann’s constant. Ideal Gas Behavior

37. Review for Test 3 Introduction Section 0 Lecture 1 Slide 37 Lecture 27 Slide 37 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 The specific heat capacity of a material is the quantity of heat needed to change a unit mass of the material by a unit amount in temperature. –For example, to change 1 gram by 1 Celsius degree. –It is a property of the material, determined by experiment. –The specific heat capacity of water is 1 cal/g  C  : it takes 1 calorie of heat to raise the temperature of 1 gram of water by 1  C. We can then calculate how much heat must be absorbed by a material to change its temperature by a given amount: Q = mc  T whereQ = quantity of heat m = mass c = specific heat capacity  T = change in temperature Heat and Specific Heat Capacity

38. Review for Test 3 Introduction Section 0 Lecture 1 Slide 38 Lecture 27 Slide 38 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 If the specific heat capacity of ice is 0.5 cal/g  C°, how much heat would have to be added to 200 g of ice, initially at a temperature of -10°C, to raise the ice to the melting point? a)1,000 cal b)2,000 cal c)4,000 cal d)0 cal m = 200 g c = 0.5 cal/g  C° T = -10°C Q = mc  T = (200 g)(0.5 cal/g  C°)(10°C) = 1,000 cal (heat required to raise the temperature)

39. Review for Test 3 Introduction Section 0 Lecture 1 Slide 39 Lecture 27 Slide 39 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 When an object goes through a change of phase or state, heat is added or removed without changing the temperature. Instead, the state of matter changes: solid to liquid, for example. The amount of heat needed per unit mass to produce a phase change is called the latent heat. –The latent heat of fusion of water corresponds to the amount of heat needed to melt one gram of ice. –The latent heat of vaporization of water corresponds to the amount of heat needed to turn one gram of water into steam. Phase Changes and Latent Heat + + + + + + + + + Solid

40. Review for Test 3 Introduction Section 0 Lecture 1 Slide 40 Lecture 27 Slide 40 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 If the specific heat capacity of ice is 0.5 cal/g  C°, how much heat would have to be added to 200 g of ice, initially at a temperature of -10°C, to completely melt the ice? a)1,000 cal b)14,000 cal c)16,000 cal d)17,000 cal L f = 80 cal/g Q = mL f = (200 g)(80 cal/g) = 16,000 cal (heat required to melt the ice) Total heat required to raise the ice to 0 °C and then to melt the ice is: 1,000 cal + 16,000 cal = 17,000 cal = 17 kcal

41. Review for Test 3 Introduction Section 0 Lecture 1 Slide 41 Lecture 27 Slide 41 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 A hot plate is used to transfer 400 cal of heat to a beaker containing ice and water; 500 J of work are also done on the contents of the beaker by stirring. What is the increase in internal energy of the ice-water mixture? a)900 J b)1180 J c)1680 J d)2180 J W = -500 J Q = 400 cal = (400 cal)(4.19 J/cal) = 1680 J  U = Q - W = 1680 J - (-500 J) = 2180 J

42. Review for Test 3 Introduction Section 0 Lecture 1 Slide 42 Lecture 27 Slide 42 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 A hot plate is used to transfer 400 cal of heat to a beaker containing ice and water; 500 J of work are also done on the contents of the beaker by stirring. How much ice melts in this process? a)0.037 g b)0.154 g c)6.5 g d)27.25 g L f = 80 cal/g = (80 cal/g)(4.19 J/cal) = 335 J/g  U = mL f m =  U / L f = (2180 J) / (335 J/g) = 6.5 g

43. Review for Test 3 Introduction Section 0 Lecture 1 Slide 43 Lecture 27 Slide 43 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 The Flow of Heat There are three basic processes for heat flow: –Conduction –Convection –Radiation

44. Review for Test 3 Introduction Section 0 Lecture 1 Slide 44 Lecture 27 Slide 44 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 The Flow of Heat –In conduction, heat flows through a material when objects at different temperatures are placed in contact with one another.

45. Review for Test 3 Introduction Section 0 Lecture 1 Slide 45 Lecture 27 Slide 45 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 –In convection, heat is transferred by the motion of a fluid containing thermal energy. Convection is the main method of heating a house. It is also the main method heat is lost from buildings. The Flow of Heat

46. Review for Test 3 Introduction Section 0 Lecture 1 Slide 46 Lecture 27 Slide 46 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 The Flow of Heat –In radiation, heat energy is transferred by electromagnetic waves. The electromagnetic waves involved in the transfer of heat lie primarily in the infrared portion of the spectrum. Unlike conduction and convection, which both require a medium to travel through, radiation can take place across a vacuum. For example, the evacuated space in a thermos bottle. The radiation is reduced to a minimum by silvering the facing walls of the evacuated space.

47. Review for Test 3 Introduction Section 0 Lecture 1 Slide 47 Lecture 27 Slide 47 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3 Heat Engines and the Second Law

48. Review for Test 3 Introduction Section 0 Lecture 1 Slide 48 Lecture 27 Slide 48 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Test 3 Review Concepts Concepts and Terms to Be Familiar With Be able to explain what a heat engine is and what the components of work, high temperature reservoir and low temperature reservoir. What is efficiency of a heat engine? Of a Carnot engine? Heat Engines and the Second Law

49. Review for Test 3 Introduction Section 0 Lecture 1 Slide 49 Lecture 27 Slide 49 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Heat Engines It is a device that uses input heat to generate useful work. From the 1 st Law (Conservation of Energy) In cyclic engines we return to the original state every cycle so What is a heat engine?

50. Review for Test 3 Introduction Section 0 Lecture 1 Slide 50 Lecture 27 Slide 50 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Heat Engines All heat engines share these main features of operation: –Thermal energy (heat) is introduced into the engine. –Some of this energy is converted to mechanical work. –Some heat (waste heat) is released into the environment at a temperature lower than the input temperature. What is a heat engine?

51. Review for Test 3 Introduction Section 0 Lecture 1 Slide 51 Lecture 27 Slide 51 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Efficiency Efficiency is the ratio of the net work done by the engine to the amount of heat that must be supplied to accomplish this work. Or from the 1st Law

52. Review for Test 3 Introduction Section 0 Lecture 1 Slide 52 Lecture 27 Slide 52 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 A heat engine takes in 1200 J of heat from the high- temperature heat source in each cycle, and does 400 J of work in each cycle. What is the efficiency of this engine? a)33% b)40% c)66% Q H = 1200 J W = 400 J e = W / Q H = (400 J) / (1200 J) = 1/3 = 0.33 = 33%

53. Review for Test 3 Introduction Section 0 Lecture 1 Slide 53 Lecture 27 Slide 53 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Carnot Efficiency The efficiency of Carnot’s ideal engine (one using an ideal gas with PV=Nk B T) is called the Carnot efficiency and is given by: This is the maximum efficiency possible for any engine taking in heat from a reservoir at absolute temperature T H and releasing heat to a reservoir at temperature T C. This provides a useful limiting case. Even Carnot’s ideal engine is less than 100% efficient.

54. Review for Test 3 Introduction Section 0 Lecture 1 Slide 54 Lecture 27 Slide 54 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Second Law of Thermodynamics You can’t recover all heat losses. You can’t win in Vegas. No engine, working in a continuous cycle, can take heat from a reservoir at a single temperature and convert that heat completely to work. Therefore, no engine can have a greater efficiency than a Carnot engine operating between the same two temperatures. Define entropy (something that measures randomness or disorder in an object) to take account of this. Heat (random motion) is a special form of energy that cannot be fully (with complete efficiency) transformed to other forms of energy. This leads to various forms of the Second Law of Thermodynamics.

55. Review for Test 3 Introduction Section 0 Lecture 1 Slide 55 Lecture 27 Slide 55 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 A Third Statement of The Second Law of Thermodynamics Entropy remains constant in reversible processes but increases in irreversible processes. The entropy of a system decreases only if it interacts with some other system whose entropy is increased in the process. –This happens, for example, in the growth and development of biological organisms. The entropy of the universe or of an isolated system can only increase or remain constant. Its entropy can never decrease.

56. Review for Test 3 Introduction Section 0 Lecture 1 Slide 56 Lecture 27 Slide 56 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 A heat pump uses 200 J of work to remove 300 J of heat from the lower-temperature reservoir. How much heat would be delivered to the higher- temperature reservoir? a)100 J b)200 J c)300 J d)500 J W = 200 J Q C = 300 J Q H = W + Q C = 200 J + 300 J = 500 J