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Physics of Technology PHYS 1800 Lecture 27 Introduction Review for Test 3 Section 0 Lecture 1 Slide 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 1 PHYSICS OF TOF ECHNOLOGY - PHYS 1800 PHYSICS TECHNOLOGY ASSIGNMENT SHEET Spring 2009Spring Assignment Sheet 2009 Date Day Lecture Chapter Feb 16 M Presidents Day 17 Tu Angular Momentum (Virtual Monday) 18 W Review 19 H Test 2 20 F* Static Fluids, Pressure Feb 23 M Flotation 25 W Fluids in Motion 27 F* Temperature and Heat Mar 2 M First Law of Thermodynamics 4 W Heat flow and Greenhouse Effect 6 F* Climate Change Mar 9-13 M-F Spring Break Mar 16 M Heat Engines 18 W Power and Refrigeration 20 F* Electric Charge Mar 23 M Electric Fields and Electric Potential 25 W Review 26 H Test 3 27 F* Electric Circuits Mar 30 M Magnetic Force Review Apr 1 W Electromagnets 3 F Motors and Generators Apr 6 M Making Waves 8 W Sound Waves 10 F* E-M Waves, Light and Color Apr 13 M Mirrors and Reflections Introduction Section 0 Lecture 1 Slide 2 15 W Refraction and Lenses 17 F* Telescopes and Microscopes Apr 20 M Review 22 W Seeing Atoms 24 F The really BIG & the really small INTRODUCTION TO Modern Physics PHYX 2710 May 1 F Final Exam: 09:30-11:20am No Class 8 5-8 5-8 9 9 9 10 10 10 No Classes 11 11 12 12 13 9-12 13 14 9-12 14 15 15 16 17 17 17 1-17 18 (not on test) 21 (not on test) Homework Due - 6 7 8 - 9 10 11 No test week 12 Fall 2004 * = Homework Handout *Homework Handout Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 2 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 Introduction Section 0 Lecture 1 Slide 3 the handout. 5. Test is Thursday March 26 1:30-2:45 in ESLC 46. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 3 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3 Introduction Section 0 Lecture 1 Slide 4 Introduction and Review INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 4 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 Introduction Section with 0 Lecture 1 Slide 5 • How things interact strong nuclear force • Random collections of objects—a temperature, T INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 5 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/s2) Force— what is required to change to motion of a body (MLT-2 or kg-m/s2 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. (ML2T-2 or kg m2/s2 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 mv2 Potential Energy is the energy associated with an objects position. Gravitational potential energy PEgravity=mgh Spring potential energy PEapring= -kx Momentum— the potential of an object to induce motion in another object (MLT-1 or kg-m/s) Introduction Section 0 Lecture 1 Slide 6 Angular Momentum and Rotational Energy— the equivalent constants of motion for rotation (MT-1 or kg/s) and (MLT-2 or kg m/s2 or N) INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 6 Newton’s Laws in Review • 1st Law —a special case of the 2nd Law for statics, with a=0 or Fnet=0 • An objects velocity remains unchanged, unless a force acts on the object. • 2nd Law (and 1st 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. F ma units : 1 newton = 1 N = 1 kg m s2 • Introduction Section 0 Lecture 1 Slide 7 3rd Law —Forces come from interactions with other objects. • For every action (force), there is an equal but opposite reaction (force). INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 7 Conservation of Energy Energy 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. Introduction Section 0 Lecture 1 Slide 8 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Time Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 8 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. v Fnet ma m t Fnet t mv • 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. Introduction Section 0 Lecture 1 Slide 9 • The momentum of the object is the mass of the object times its velocity. p mv INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 9 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. impulse = change in momentum = p In analogy, Introduction Section 0 Lecture 1 work INTRODUCTION TO Modern Physics PHYX 2710 Slide 10 = change in energy = ΔE Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 10 Formulas We Know and Love Formulas as They Will Appear on the Test Sheet d vo t a t v a d 1 2 f o t t 2 do t v f vo t 1 2 f 2 o ma mb r2 Ra3 Rb3 Gma Ta2 Tb2 4 2 G=6.67·10-11 N-m2/kg2 g=9.8 m/s2 PE gravity mgh Fgravity G t f o t F ma W F d net I Fl KEtrans 12 mv 2 KErot 12 I 2 p F t L t Introduction Section 0 Lecture 1 Slide p mv L I W I mr 2 Power INTRODUCTION TO Modern Physics PHYX 2710 t v2 ac r 11 Felastic k x PEelastic 12 k x 2 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 11 Physics of Technology PHYS 1800 Lecture 27 Introduction Review for Test 3 Section 0 Lecture 1 Slide 12 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 12 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 Introduction Section 0 Lecture 1 Slide 13 transfer: conduction, convection and radiation. Be able to explain what a heat engine is and what the components of work, high INTRODUCTION TO Modern Physics PHYX 2710 temperature reservoir and low temperature reservoir. Fall 2004 What is efficiency of a heat engine? Of a Carnot engine? Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 13 Formulas We Know and Love New Formulas as They Will Appear on the Test Sheet PF/A kB=1.38 10-23 J/K flow rate v A m /V PV Nk BT P 12 v 2 g h constant W P V Q m c T e W / QH Introduction Section 0 Lecture 1 QH QC QH eCarnot TH TC TH Slide 14 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 14 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3 Introduction Section 0 Lecture 1 Slide 15 Fluids and Pressure INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 15 Test 3 Review Concepts Fluids and Pressure 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. Introduction Section 0 Lecture 1 Slide 16 Understand the difference between laminar and turbulent flow. Understand Bernoulli’s Principle as a fluid form of the conservation of energy. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 16 States of Matter Introduction Section 0 Lecture 1 Slide 17 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 17 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/m2 = 1 Pa (pascal) – Pressure is the quantity that determines whether the soil will yield. Introduction Section 0 Lecture 1 Slide INTRODUCTION TO Modern Physics PHYX 2710 F P A 18 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 18 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 Introduction Section 0 Lecture 1 Slide 19 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 19 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 fluid. Introduction Section 0 Lecture 1the Slide 20 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 20 • • • • • • • 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 Introduction Section 0 Lecture 1 Pascal’s Principle for Gases Slide 21 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 21 • • • • + Section 0 + Lecture 1 + + INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 + Physics of Technology—PHYS 1800 Spring 2009 Pascal’s Principle for Liquids + + + + + + + + + + + + Introduction + + + + + + + • 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 + + + + + + • • • + + Slide + 22 + + + Review for Test 3 Lecture 27 Slide 22 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. Introduction Section 0 Lecture 1 Slide 23 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 23 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. Introduction Section 0 The volume of the fluid displaced is directly related to the weight of the fluid displaced. Lecture 1 Slide 24 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Weight mg Vdg Volume Ah Excess Pressure P W dgAh dgh A a Review for Test 3 Lecture 27 Slide 24 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. Introduction Section 0 Lecture 1 Slide 25 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 25 Laminar vs Turbulent Flow • 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. Introduction Section 0 Lecture 1 Slide 26 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 26 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? Work KE PE E constant Total • Bernoulli’s principle applies 1 2 conservation of energy to the flow of PV mv mgh E constant fluids: 2 • The sum of the pressure plus the • kinetic energy per unit volume of 1 2 0 Lecture 1 Slide 27 • aIntroduction flowing Section fluid must remain P v gh E/V constant 2 constant. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 27 Pressure Changes with Area 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 dv2 constant, the pressure must be larger where the fluid speed is smaller (h is fixed). • If the speed increases, the pressure decreases. (This goes Introduction 0 Lecture 1 Slide 28 against ourSection intuition.) • This can be shown using vertical open pipes as pressure gauges. • The height of the column of water is proportional to the pressure. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 28 Physics of Technology PHYS 1800 Lecture 27 Introduction Review for Test 3 Section 0 Lecture 1 Slide 29 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 29 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3 Introduction Section 0 Lecture 1 Slide 30 Temperature and Heat INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 30 Test 3 Review Concepts Temperature and Heat 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. Introduction Section 0 Lecture 1 Slide 31 Be able to qualitatively explain the difference between the three forms of heat transfer: conduction, convection and radiation. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 31 Dennison’s Laws Thermal Poker (or How to Get a Hot Hand in Physics) • 0th Law: Full House beats Two Pairs • 1st Law: We’re playing the same game (but with a wild card) • 2nd Law: You can’t win in Vegas. • 3rd Law: In fact, you always loose. • 0th Law: Defines Temperature • 1st Law: Conservation of Energy (with heat) • 2nd Introduction Section 0 Lecture 1 Slide 32 Law: You can’t recover all heat losses (or defining entropy) INTRODUCTION TO Modern Physics PHYX 2710 • Fall 2004 3rd Law: You can never get to absolute 0. Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 32 Heat • 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 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. Introduction Section 0 Lecture 1 Slide 33 Gas: No equilibrium position, no oscillations, atoms are free and move in perpetual high-speed “zig-zag” dance punctuated by collisions. solid liquid INTRODUCTION TO Modern Physics PHYX 2710 gas Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 33 Temperature and Heat • 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. Introduction Section 0 Lecture Heat is a form of energy. (Here comes conservation of energy!!!) 1 Slide 34 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 34 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 theIntroduction distance the Section 0 piston Lecture 1 moves: Slide 35 W = Fd = (PA)d = PV INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 35 Ideal Gas Behavior • 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 Introduction Section 0 where N is the number of molecules k is Lecture 1 and Slide 36 Boltzmann’s constant. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 36 Heat and Specific Heat Capacity • 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/gC: it takes 1 calorie of heat to raise the temperature of 1 gram of water by 1C. • We can then calculate how much heat must be absorbed by a material to change its temperature by a given amount: Q =Introduction mcT Section 0 where Lecture INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 1 Slide 37 Q = quantity of heat m = mass c = specific heat capacity T = change in temperature Review for Test 3 Lecture 27 Slide 37 If the specific heat capacity of ice is 0.5 cal/gC°, 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) b) c) d) 1,000 cal 2,000 cal 4,000 cal 0 cal Introduction m = 200 g c = 0.5 cal/gC° T = -10°C Q = mcT (200 g)(0.5 cal/gC°)(10°C) Section 0 Lecture 1 =Slide 38 = 1,000 cal (heat required to raise the temperature) INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 38 Phase Changes and Latent Heat • 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. Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 + INTRODUCTION TO Modern Physics PHYX 2710 + Slide 39 + + + Lecture 1 + Section 0 + Introduction + + Solid Lecture 27 Slide 39 If the specific heat capacity of ice is 0.5 cal/gC°, 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? Lf = 80 cal/g a) b) c) d) 1,000 cal 14,000 cal 16,000 cal 17,000 cal Introduction Section 0 Lecture 1 Q = mLf = (200 g)(80 cal/g) = 16,000 cal (heat required to melt the ice) Slide 40 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 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 40 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) b) c) d) 900 J 1180 J 1680 J 2180 J Introduction Section 0 Lecture 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 W = -500 J Q = 400 cal = (400 cal)(4.19 J/cal) = 1680 J Slide 41 U = Q - W = 1680 J - (-500 J) = 2180 J Review for Test 3 Lecture 27 Slide 41 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) b) c) d) 0.037 g 0.154 g 6.5 g 27.25 g Introduction Section 0 Lecture 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Lf = 80 cal/g = (80 cal/g)(4.19 J/cal) = 335 J/g U Slide 42 = mLf m = U / Lf = (2180 J) / (335 J/g) = 6.5 g Review for Test 3 Lecture 27 Slide 42 The Flow of Heat • There are three basic processes for heat flow: – Conduction – Convection – Radiation Introduction Section 0 Lecture 1 Slide 43 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 43 The Flow of Heat Q T kA t L – In conduction, heat flows through a material when objects at different temperatures are placed in contact with one another. Introduction Section 0 Lecture 1 Slide 44 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 44 The Flow of Heat – 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. Introduction Section 0 Lecture 1 Slide 45 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 45 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. Q t A B T Introduction Section 0 4Lecture 1 Slide 46 B 5.7 10 8 W / m 2 K 4 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 46 Physics of Technology PHYS 1800 Lecture 27 Review for Test 3 Introduction Section 0 Lecture 1 Slide 47 Heat Engines and the Second Law INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 47 Test 3 Review Concepts Heat Engines and the Second Law 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? Introduction Section 0 Lecture 1 Slide 48 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 48 Heat Engines What is a heat engine? It is a device that uses input heat to generate useful work. e From the 1st Law (Conservation of Energy) W QH W Qnet U In cyclic engines we return to the original state every cycle so U 0 Introduction Section 0 and W QH QC Lecture 1 Slide 49 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 49 Heat Engines What is a heat engine? 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 Introduction Sectionat 0 aLecture 1 Slide 50 temperature lower than the input temperature. QH W QC INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 50 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. W e QH Or from the 1st Law QH Section Q0C Introduction e Lecture 1 Slide 51 QH INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 51 A heat engine takes in 1200 J of heat from the hightemperature heat source in each cycle, and does 400 J of work in each cycle. What is the efficiency of this engine? a) b) c) 33% 40% 66% QH = 1200 J W = 400 J e = W /Introduction QH Section 0 Lecture 1 = (400 J) / (1200 J) = 1/3 = 0.33 = 33% Slide 52 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 52 Carnot Efficiency • The efficiency of Carnot’s ideal engine (one using an ideal gas with PV=NkBT) is called the Carnot efficiency and is given by: QH QC TH TC eC QH TH • This is the maximum efficiency possible for any engine taking in heat from a reservoir at absolute temperature TH and releasing heat to a reservoir at temperature TC. Introduction Section 0 Lecture 1 Slide 53 • This provides a useful limiting case. • Even Carnot’s ideal engine is less than 100% efficient. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 53 Second Law of Thermodynamics 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. • 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 Introduction Section 0between Lecture 1 the Slide 54 engine operating same two temperatures. • Define entropy (something that measures randomness or disorder in an object) to take account of this. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 54 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 Introduction Section 0 Lecture 1 Slide 55 system can only increase or remain constant. Its entropy can never decrease. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 55 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 highertemperature reservoir? a) b) c) d) 100 J 200 J 300 J 500 J W = 200 J QC = 300 J Section 0 Lecture 1 Introduction QH = W + QC = 200 J + 300 J = 500 J Slide 56 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review for Test 3 Lecture 27 Slide 56