 Thermal systems are designed to move heat energy from warmer regions to cooler regions  Usually to help remove excessive heat (ex. radiator of car)  Temperature difference (∆T) is the prime mover/force-like quantity in thermal systems similar to voltage in electrical systems and force in mechanical systems.  Heat energy always flow from high to low heat energy regions  i.e. system tries to reach equilibrium so that temp is the same across the entire system

 Temperature depends on the presence or absence of heat  Measured either in Fahrenheit(F) or Celsius(C)  If measuring temperature than written as °F or °C (degree symbol is written BEFORE symbol)  If measuring temperature difference(change in temperature) then must write C ° or F ° (placement of ° symbol changes so it is written AFTER the symbol)  Temperature is a scalar quantity  It is a measure of the amount of average energy that molecules in motion have  The more motion, the greater the energy, the higher the temperature (cool to warm to hot)

1a. Thermometers  Most common device is the liquid-in-glass thermometer  Glass bulb containing capillary tube filled with liquid (most commonly alcohol…or mercury)  As temp increases, fluid expands and rises up capillary tube  Height of fluid is measured using scale on outer surface of glass – either Celsius(SI/metric unit) or Fahrenheit(English unit)

2a. Thermocouples  Thermocouple is another type of device used to measure temperature (temperature difference)  Depends on changes in electrical properties of certain metals (ex. Iron, Constantan, Chromel)  when 2 of these metals are twisted together (like a twist-tie) they make a thermocouple junction  A small voltage develops across the connecting joint when the other ends of the wires are at different temperatures  Amount of voltage generated depends on the types of metal used and the temperature difference being measured

2a. Thermocouples cont.  2 thermocouple junctions connected together make a thermocouple thermometer  Contains 2 junctions(T R and T) connected to a Voltmeter  One of the junctions is a reference junction (T R )  The other junction is the measurement junction (T)  When the junction of the two metals for T R and T is heated or cooled a voltage is produced that can be correlated back to the actual temperature.  If temp at T is greater than at T R,a higher positive voltage will be read by the voltmeter. A negative voltage will be read if temp at T< T R WIRE A

1b. Thermometer Scales and Calibration  To ensure proper measurements thermometers must first be calibrated  Done using 2 reference points – boiling and freezing  In Celsius : Boiling pt water = 100°C(at sea level) Freezing pt water = 0°C which means 100° Celsius degree(°) points on scale between boiling and freezing  In Fahrenheit : Boiling pt of water = 212F and Freezing pt water = 32F which means 180 Fahrenheit degree points between boiling and freezing  Now complete this : Student Exercises Q1-8 on pp in workbook. YOU MUST COPY EACH QUESTION and draw the table for Q#2 and use GFS for Q#5.

1c. Converting Among Celsius and Fahrenheit Scales (absolute values)  To convert from Fahrenheit to Celsius: T(°C) = 5/9[T(°F) – 32°]  To convert from Celsius to Fahrenheit: T(°F) = 9/5 T(°C) + 32° PRACTICE: Now try Example “1a” on the last slide…

1d. Converting Among Celsius and Fahrenheit Scales For Temperature Difference  With temp.difference you must use relationship: 1C° = 1.8F°  Set up correct proportion depending on given PRACTICE: Now try Examples “1b & c” on the last slide...

1a) Outside temperature is 42°C. Use GFS to find what is the temperature in °F? b) The next day the temperature drops to 93.2 °F. Use GFS to find the temperature change/difference? c) Convert your answer from “b” to C° PRACTICE WORK: Complete Q1-6 on pg.101 in workbook using GFS. Read the examples on pp if you need help. Note: This work must all be done by the end of class