PHYSICS Part I: Heat and GasesHong Kong Diploma of Secondary Education (HKDSE) Notes & Exercises Chapter 1 to 4 ANDY WONG S.T. .. Mean K................................................ van der Waals’ equation** ..................................... 12 6...................... 12 9.................................................................... 13 11............... Convection .......................................................... Ideal gas law ......... Departure from Boyle’s law for real gas at high pressure ................. Molecular motion and conduction............................... 5 4........................................................ Radiation ................................................................................................. 10 8.............................. 9 6........................... Some deductions from the kinetic theory ................................................... of a gas molecule ........................................ 9 3................................ Thermometers ................................ Importance of high specific heat capacity of water .................................................................................................... Heat capacity ................................. 10 7........................ 13 12.................................. 10 1......... Assumptions in kinetic theory model.........................................................TABLE OF CONTENTS CHAPTER 1 TEMPERATURE AND INTERNAL ENERGY .......................................................... General gas law ......... 8 5. Specific heat capacity ............ 8 8....... 8 CHAPTER 2 CHANGE OF STATE .......................... The pressure law....... Temperature ................... 13 2 .................................................................................................................. 13 13.................................. Greenhouse and vacuum flask ......................... Latent heat ...................................................................................... Boyle’s law ......................................................................................... Temperature scales ............ 9 1.................................................... 10 9.......... Pressure ........................................ 12 1................................ 12 4................... Mixture ............................... 13 10........... 12 2................................ Maxwell-Boltzmann distribution for molecular speeds ............................................ Applications of conductors and insulators of heat ................................................... Cooling curve ...... 13 14................... Examples of convection of heat ................... 10 5................................ 10 *CHAPTER 4 GAS LAW AND KINETIC THEORY......................................................... Evaporation and boiling ... 10 3............................................................................................................................................................ Specific latent heat of vaporization .......................... 12 8........... Specific latent heat of fusion ................................................... 12 5.......... 10 6............. Conduction ..... States of matter ............................................................................... Heat and internal energy ............................... 8 6..................................................................................... Conductivity of heat ................................................................................................. 10 4........................................ Absorbers and emitters of radiation ................................................................ 4 2...E...................................... 9 2....................................................................................... 9 5.......................................................................................................................................... Charles’ law...................................................................................................... 4 1................ Intermolecular forces** ............ 13 15............. 9 4...... Kinetic theory of gas (statistical mechanics) ................................................................ 10 2............... Brownian motion................................................................. 8 7................... 12 3................................. 9 CHARTER 3 TRANSFER PROCESS ....................................................... 4 3.............................. 12 7. ................. Isotherm of real gas** ........... 3 ..... 13 *These topics are not required in physics part of HKDSE Combined Science curriculum............................Part I 16...................... t. e. The lower fixed point is 0C. Temperature range is then divided into 100 equal divisions called degree Celsius. Sense of touch (by skin) cannot detect the exact temperature. 4 . When temperature is above absolute zero. i. these particles are constantly under random motion and have kinetic energy. It is also subjective and inaccurate. solubility of a solute.p. etc. There are 3 commonly used temperature scales: (a) Celsius scale Lower fixed point (or ice point) is the temperature of pure melting ice at one standard temperature and pressure (s. A stable fixed point should be easily and accurately reproducible. B. Temperature is a measure of average kinetic energy of the particles. resistance of a metal. Thermometric properties Thermometric properties are physical properties that change with temperature. and the upper fixed point is 100C.p. a lower fixed point and an upper fixed point. Upper fixed point (or steam point) is the temperature of pure boiling water at 1 s. As a measure of average kinetic energy of molecules Matter is composed of atoms. A. molecules or ions.).g.CHAPTER 1 TEMPERATURE AND INTERNAL ENERGY 1. Temperature scales A temperature scale can be obtained by: (1) Choosing two fixed points. but only the differences in temperature. (2) The range between this two fixed points are divided into a number of equal divisions called degree.e. Temperature Temperature is a physical property that measures the degree of hotness (or coldness) of an object. written as C.t. 2. volume of a gas. thus unreliable. Thermometers A. 5 . written as K. A digital one uses an electronic device to measure temperature accurately within a short time. It is most commonly used in the United States. A conventional one has a constriction in the capillary tube near the bulb to prevent the mercury column from falling back into the bulb. The temperature interval of 1K is the same as that of 1C. Types of thermometers (a) Liquid-in-glass thermometer It consists of a closed capillary tube with a glass bulb at one end. and capillary tube is made very narrow to improve sensitivity of the thermometer. Kelvin scale and Celsius scale can be interconverted by: Fahrenheit temperature = Celsius temperature + 32 3. written as F. poisonous Alcohol-in-glass thermometer -100C to 110C Slower Colourless (usually with dye) Flammable (b) Clinical thermometer It is designed to measure human body temperature. The bulb is filled with a thermometric liquid which expands and contracts with temperature. It should expand or contract linearly. Wall of glass bulb is usually very thin to increase rate of heat transfer.Part I (b) Kelvin scale The unit used is kelvin. Mercury-in-glass thermometer Working range Response to temperature change Appearance Concerns ~30C to 400C Quicker Silvery More costly. 0K is the lowest possible temperature of matter and is called absolute zero. It only measures a small temperature range but is quite sensitive. Kelvin scale and Celsius scale can be interconverted by: Kelvin temperature = Celsius temperature + 273 (c) Fahrenheit scale The unit used is degree Fahrenheit. A large angle of deflection indicates a higher temperature. The bimetallic strip is often wound to a spiral. But.g. ice water at 0C) and the other is placed where the temperature to be measured. which curls when heated and rotates a pointer attached to its end. It is often used in industry to measure the temperatures of furnaces or in geography to measure the temperatures of lava from volcanoes. the reading of the ammeter can show the temperature measured by the junction. the strip bends. (e) Thermistor thermometer It works in a way similar to that of a resistance thermometer. the reading of the ammeter thus decreases.(c) Rotary thermometer It consists of a bimetallic strip made of two different metal strips joined together side by side. It is widely used in industry to measure temperatures of ovens and engine parts. After calibration. It can accurately measure a wide range of temperature. A larger temperature difference between the two junctions will cause a larger current to flow through the circuit. 6 . It is commonly used in electrical appliances e.g. As temperature increases. (d) Resistance thermometer It consists of a coil of metal wire connected to an ammeter and a battery. the resistance of the thermistor decreases. the resistance of the metal increases. the reading of the ammeter thus increases. but an electronic component called thermistor is used instead of the coil of metal wire. It is often used in large freezers and ovens. One junction is kept at a constant temperature (e. Two junctions are formed by twisting the ends of different metal wires together. current passing through the coil drops. It is robust and has a wide working temperature range from -50C to 300C. and its response rate is fast. cookers for temperature control. It has a narrow working temperature range from -50C to 150C. Since two different metals expand to different extents under heat. its calibration is not an easy task. This type of thermometer measures a wide range of temperatures from -250C to 2300C. but calibration should be done each time before usage. When the temperature increases. but it is very sensitive. (f) Thermocouple thermometer It consists of three pieces of wire in which two are of the same metal and the other one is different. Objects emit more infrared radiation as the temperature rises. It is also used in measuring temperatures up to 4000C in industry. It can measure temperature ranging from 10C to 50C. It is used to measure human body temperature or water temperature in an aquarium. length of liquid column) corresponding to the temperature we measure. The temperature can then be found by algebraic method or graphical method.g. with the help of infrared thermograph. 7 . It is commonly used in measuring human body temperature.g. Find the increase in length of the alcohol column. which is 36. For thermometric properties that do not behave linearly. B. A student calibrates an unmarked alcohol-in-glass thermometer and obtains the following: In pure melting ice In pure boiling water length of alcohol column / cm 4 28 (a) The temperature now rises to 10C. (h) Liquid crystal thermometer It consists of liquid crystals that change colour with temperature. 1. we need to plot a calibration graph to determine the temperature measured. Hotter regions will have a red colour and colder regions will have a blue one. and record the level of physical property (e.5C. what will be the length of alcohol column? Solution (a) As alcohol expands linearly with temperature. e. we have to mark two fixed points on the thermometer first. Calibration of thermometers For thermometric properties that behave linearly. and objects at a great distance. (b) What is the temperature measured by the thermometer when the length of alcohol column is 16cm? (c) If the thermometer is used to measure human body temperature. we can also detect the temperature distribution of an object. In addition. The infrared thermometer measures the temperature of an object by measuring the infrared radiation emitted.Part I (g) Infrared thermometer Any object whose temperature is above absolute zero emits infrared radiation. Mixture Law of conservation of energy 8. Heat and internal energy Ways to increase internal energy Power 5. Importance of high specific heat capacity of water 8 .4. Heat capacity 6. Specific heat capacity Measurement of specific heat capacity 7. Specific latent heat of vaporization Determination of specific latent heat of vaporization of water 6.Part I CHAPTER 2 CHANGE OF STATE 1. Cooling curve 3. Specific latent heat of fusion Determination of specific latent heat of fusion of ice 5. States of matter 2. Latent heat As a measure of change of potential energy of molecules 4. Evaporation and boiling Factors affecting the rate of evaporation 9 . Greenhouse and vacuum flask 10 . Conduction 2. Radiation 8. Molecular motion and conduction Factors affecting the rate of conduction 4. Convection 6. Absorbers and emitters of radiation 9. Applications of conductors and insulators of heat 5.CHARTER 3 TRANSFER PROCESS 1. Examples of convection of heat 7. Conductivity of heat 3. Part I 11 . General gas law 6. Brownian motion 8. 7. Boyle’s law 3. Assumptions in kinetic theory model 12 . Ideal gas law Mean separation between gas molecules at s.t. The pressure law 4.*CHAPTER 4 GAS LAW AND KINETIC THEORY 1.p. Charles’ law 5. Pressure Atmospheric pressure Gas pressure 2. Intermolecular forces** 14. of a gas molecule 11.Part I 9. van der Waals’ equation** 15. Maxwell-Boltzmann distribution for molecular speeds 13. Isotherm of real gas** 13 . Kinetic theory of gas (statistical mechanics) 10.E. Some deductions from the kinetic theory 12. Departure from Boyle’s law for real gas at high pressure 16. Mean K.