Slide 1 / 163 Slide 2 / 163 Thermal Physics www.njctl.org Slide 3 / 163 Slide 4 / 163 Thermal Physics · Temperature, Thermal Equilibrium and Thermometers · Thermal Expansion · Heat and Temperature Change · Thermal Equilibrium : Heat Calculations · Phase Transitions · Heat Transfer · Gas Laws Temperature, Thermal Equilibrium · Kinetic Theory Click on the topic to go to that section · Internal Energy and Thermometers · Work in Thermodynamics · First Law of Thermodynamics · Thermodynamic Processes · Second Law of Thermodynamics · Heat Engines · Entropy and Disorder Return to Table of Contents Slide 5 / 163 Slide 6 / 163 Temperature and Heat Temperature Here are some definitions of temperature: In everyday language, many of us use the terms temperature · A measure of the warmth or coldness of an object or substance with and heat interchangeably reference to some standard value. But in physics, these terms have very different meanings. · Any of various standardized numerical measures of this ability, such Think about this… as the Kelvin, Fahrenheit, and Celsius scale. · When you touch a piece of metal and a piece of wood both · A measure of the ability of a substance, or more generally of any resting in front of you, which feels warmer? · When do you feel warmer when the air around you is 90°F physical system, to transfer heat energy to another physical system. and dry or when it is 90°F and very humid? · A measure of the average kinetic energy of the particles in a sample · In both cases the temperatures of what you are feeling is of matter, expressed in terms of units or degrees designated on a the same. Why then are you feeling a difference? standard scale. In this unit, we will learn about temperature, heat, and the laws of thermodynamics that relate heat, mechanical work We'll consider each of these definitions in this unit. and other forms of energy. Slide 7 / 163 Slide 8 / 163 Thermometers and Thermal Equilibrium Thermometers To measure temperature of a substance, we need... 1. A measuring device (Thermometer) that changes visibly and is calibrated to a scale. Thermometers relate the change in a physical property of substance to temperature. Examples include: > The change of volume of a gas or liquid > The change in length of a metal strip or wire > The light or infrared radiation emitted by an object 2. To bring the Thermometer into contact with the substance > When the thermometer has settled on a value, we say that the thermometer and the substance are in Thermal Equilibrium Slide 9 / 163 Slide 10 / 163 Temperature Scales Temperature Scales Recall that temperature can be defined as... · a measure of the warmth or coldness of an object or substance with reference to some standardized numerical measures or scales Three common scales are: CO2 Solidifies · Fahrenheit (°F) - used mainly in the USA O2 Liquifies · Celsius (°C) - used in most of the world · Kelvin (K) - used in the physical sciences > also known as the Absolute Temperature Scale Kelvin Celsius Fahrenheit Slide 11 / 163 Slide 12 / 163 Temperature Conversions 1 Which temperature scale does not have negative values? A Fahrenheit Celsius # Fahrenheit B Celsius C Kelvin D All the above Celsius # Kelvin E None of the above Slide 12 (Answer) / 163 Slide 13 / 163 1 Which temperature scale does not have negative values? 2 Water freezes at 32°F. What temperature would this be on the Celsius scale? A Fahrenheit A 32 °C B Celsius B 0° C C Kelvin C 25° C D All the above C Kelvin D 212°C E None of the above Answer E 100° C [This object is a pull tab] Slide 13 (Answer) / 163 Slide 14 / 163 2 Water freezes at 32°F. What temperature would this be on the 3 Water boils at 100° C. What temperature would this be on the Celsius scale? Fahrenheit scale? A 32 °C A 32 °F B 0° C B 100° F C 25° C C 0° F B 0°C D 212°C D 212° F Answer E 100° C E 180° F [This object is a pull tab] Slide 14 (Answer) / 163 Slide 15 / 163 3 Water boils at 100° C. What temperature would this be on the 4 “Room temperature” is often taken to be 68 °F; what is this on the Fahrenheit scale? Celsius scale? A 32 °F A 34 ° C B 100° F B 37.78° C C 0° F C 5.78° C D 212° F D 212°F D 20° C Answer E 180° F E 52° C [This object is a pull tab] Slide 15 (Answer) / 163 Slide 16 / 163 4 “Room temperature” is often taken to be 68 °F; what is this on the 5 The coldest temperature recorded on earth was −89.2 °C at the Celsius scale? Soviet Vostok Station in Antarctica, on July 21, 1983. What would a Fahrenheit scale thermometer have measured? A 34 ° C B 37.78° C C 5.78° C D 20°C D 20° C Answer use TC = (TF - 32) /1.8 E 52° C [This object is a pull tab] Slide 16 (Answer) / 163 Slide 17 / 163 5 The coldest temperature recorded on earth was −89.2 °C at the 6 The coldest temperature recorded on earth was −89.2 °C at the Soviet Vostok Station in Antarctica, on July 21, 1983. What would a Soviet Vostok Station in Antarctica, on July 21, 1983. What would a Fahrenheit scale thermometer have measured? Kelvin scale thermometer have measured? TF = 1.8TC + 32 = 1.8(89.2) + 32 Answer = - 128.6 °F [This object is a pull tab] Slide 17 (Answer) / 163 Slide 18 / 163 6 The coldest temperature recorded on earth was −89.2 °C at the Thermal Equilibrium: The Zeroth Law of Soviet Vostok Station in Antarctica, on July 21, 1983. What would a Kelvin scale thermometer have measured? Thermodynamics Two objects placed in thermal contact will eventually come to the same temperature. When they do, we say they are in thermal equilibrium. The zeroth law of thermodynamics says that if two objects are each in equilibrium with a third object, they are also in thermal TK = TC + 273 equilibrium with each other. = -89.2 + 273 Answer = 183.8 K T3 T1 T2 [This object is a pull tab] That is if T1 = T3 and T2 = T3 then T1 = T2 Slide 19 / 163 Slide 20 / 163 Thermal Conductors and Insulators 7 Three objects A, B, and C initially have different temperatures TA>TB>TC. Objects A and B are separated by an insulating plate but they are in contact with object C through a conducting plate. Which of the following is true when objects A and B reach thermal equilibrium with object C? Conductors - materials that allow heat to flow easily (metals) Insulators - materials that slow or block heat flow (wood, plastic, fiberglass) A The temperatures of all three objects do not change B Object A has a higher temperature than Object B and Object C C Object C has a higher temperature than Object A and Object B D Object B has a higher temperature than Object A and Object C E All three objects have the same temperature Slide 20 (Answer) / 163 Slide 21 / 163 7 Three objects A, B, and C initially have different temperatures TA>TB>TC. Objects A and B are separated by an insulating plate but they are in contact with object C through a conducting plate. Which of the following is true when objects A and B reach thermal equilibrium with object C? E All three objects have the same Thermal Expansion A The temperatures of all three objectstemperature do not change Answer B Object A has a higher temperature than Object B and Object C C Object C has a higher temperature than Object A and Object B [This object is a pull tab] D Object B has a higher temperature than Object A and Object C E All three objects have the same temperature Return to Table of Contents Slide 22 / 163 Slide 23 / 163 Thermal Expansion Linear Expansion Suppose a rod composed of some substance has a length L0 at · Most materials expand when their temperatures increase. an initial temperature of T0. · Liquids expand in a thermometer. If the temperature is changed by ∆T, the length changes by ∆L. · A tight metal jar lid can be loosened by running it in hot water. If ∆T is not too large, ∆L is directly proportional to ∆T. · These are examples of thermal expansion. L0 T0 · We consider two types of thermal expansion: T0+∆T > Linear L = L0+∆L > Volume The change in length is ∆L = α L0 ∆T where α is the coefficient of linear expansion Slide 24 / 163 Slide 25 / 163 Linear Expansion 8 A steel rod measures 10 meters at 0° C. Given that the coefficient of linear expansion of steel is 1.2 x 10-5 per °C, what will the rod measure at 75°C? -6 Substance Coefficient of Linear Exansion α (×10 / °C) Aluminum 23.1 Diamond 1 Copper 17 Glass 8.5 Iron 11.8 Gold 14 Steel 13.2 Ice 51 Slide 25 (Answer) / 163 Slide 26 / 163 8 A steel rod measures 10 meters at 0° C. Given that the coefficient 9 A simple pendulum is made of a steel string supporting a brass sphere. The of linear expansion of steel is 1.2 x 10-5 per °C, what will the rod temperature in a room with the pendulum is increased from 15° C to 30° C. measure at 75°C? Which of the following is true about the period of oscillations? A the period doubles B the period does not unchanged L = L0 + ∆L C the period slightly increases = L0 (1+α∆T) Answer = 100(1+0.000012*75) =100.09 m D the period slightly decreases E the period increases by √2 [This object is a pull tab] Slide 26 (Answer) / 163 Slide 27 / 163 9 A simple pendulum is made of a steel string supporting a brass sphere.