Temperature in Thermal Temperature in Thermal SystemsSystems

Vocabulary Pg 91-96Vocabulary Pg 91-96(leave a space between words)(leave a space between words)

Heat energyHeat energy Temperature differenceTemperature difference

InsulatedInsulated TemperatureTemperature

ScalarScalar HeatHeat

ThermocoupleThermocouplePage 97Page 97

#1-8#1-8

Thermal systemsThermal systems Designed to move heat energy from Designed to move heat energy from

warmer regions to cooler regionswarmer regions to cooler regions

In an automobile we have a fan, water In an automobile we have a fan, water pump, radiator, hoses, thermostat, pump, radiator, hoses, thermostat,

coolant fluids, and aircoolant fluids, and air

Temperature Difference acts like a Temperature Difference acts like a ForceForce

The prime mover is The prime mover is temperature temperature differencedifference

Written: Written: ΔΔTT

Movement of heatMovement of heat

Heat always moves from warm areas Heat always moves from warm areas to coolerto cooler

This is undesirable in homes both in This is undesirable in homes both in the summer and winterthe summer and winter

Therefore we Therefore we insulateinsulate the walls to the walls to reduce in heat loss and gainreduce in heat loss and gain

What is heat? What is What is heat? What is temperature?temperature?

Temperature is a scalar quantityTemperature is a scalar quantity Measured in degrees Fahrenheit or Measured in degrees Fahrenheit or

degrees Celsiusdegrees Celsius

Heat – Form of energy found in the Heat – Form of energy found in the vibrating motion of atoms and vibrating motion of atoms and

moleculesmolecules

What is heat? What is What is heat? What is temperature?temperature?

Temperature – A measure of the Temperature – A measure of the average energy of motion of the average energy of motion of the

molecules in a substancemolecules in a substance

Hot items have high average energy Hot items have high average energy motionmotion

Cool items have low average energy Cool items have low average energy motionmotion

How does a thermometer work?How does a thermometer work?

Filled with liquid Filled with liquid such as mercury such as mercury or colored or colored alcoholalcohol

When the When the temperature of temperature of the liquid the liquid increases it increases it expandsexpands

A scale is provided to make readingsA scale is provided to make readings

Temperature ScalesTemperature Scales

Freezing point of water = 32 degreesFreezing point of water = 32 degrees Boiling point of water = 212 degreesBoiling point of water = 212 degrees

Freezing point of water = 0 degreesFreezing point of water = 0 degrees Boiling point of water = 100 degreesBoiling point of water = 100 degrees

Fahrenheit ScaleFahrenheit Scale

Celsius ScaleCelsius Scale

Fahrenheit vs. CelsiusFahrenheit vs. Celsius

Fahrenheit vs. CelsiusFahrenheit vs. Celsius

On a thermometer the scale shows On a thermometer the scale shows that 100 Celsius degrees are equal that 100 Celsius degrees are equal

to 180 Fahrenheit degreesto 180 Fahrenheit degrees 1 C1 Coo = 1.8 F = 1.8 Foo

Writing Temp or Temp DifferencesWriting Temp or Temp Differences

3232ooF is different than 32FF is different than 32Foo

Writing Temp or Temp DifferencesWriting Temp or Temp Differences

Temperatures are degrees Temperatures are degrees Celsius (Celsius (ooC) or degrees C) or degrees

Fahrenheit (Fahrenheit (ooF)F)

Temperature differences are Temperature differences are Celsius degrees (CCelsius degrees (Coo) or ) or Fahrenheit degrees (FFahrenheit degrees (Foo))

Converting from one scale to Converting from one scale to anotheranother

Converting from one scale to anotherConverting from one scale to another

Given: A temperature of 50Given: A temperature of 50ooFF Find: The same temperature in Find: The same temperature in

degrees Celsius (degrees Celsius (ooC)C)

Solution:Solution: TTooC = 5/9(TC = 5/9(TooF – 32F – 32oo)) TTooC = 5/9(50C = 5/9(50oo – 32 – 32oo))

TTooC = 5/9(18C = 5/9(18oo)) Therefore, 50Therefore, 50ooF is the same as 10F is the same as 10ooCC

Converting from one scale to anotherConverting from one scale to another Given: A temperature of 20Given: A temperature of 20ooCC

Find: The temperature in degrees Find: The temperature in degrees Fahrenheit (Fahrenheit (ooF)F)

Solution:Solution: TTooF = 9/5(TF = 9/5(TooC) + 32C) + 32oo

TTooF = 9/5(20F = 9/5(20oo)+ 32)+ 32oo

TTooF = 36F = 36oo + 32 + 32oo

TTooF = 68F = 68ooFF Therefore, 20Therefore, 20ooC is the same as 68C is the same as 68ooFF

Converting from one scale to anotherConverting from one scale to another

Given: The temperature in the room just Given: The temperature in the room just went up 11 Cwent up 11 Coo

Find: What is the temperature difference Find: What is the temperature difference in degrees Fahrenheitin degrees Fahrenheit

Solution:Solution: 1 C1 Coo = 1.8 F = 1.8 Foo

11 x 1 C11 x 1 Coo = 11 x 1.8 F = 11 x 1.8 Foo

11 C11 Coo = 19.8 F = 19.8 Foo

Converting from one scale to anotherConverting from one scale to another

Given: The temperature in the room is 68Given: The temperature in the room is 68ooF F but just went down 4 Cbut just went down 4 Coo

Find: How much the temperature Find: How much the temperature decreases in Fahrenheit.decreases in Fahrenheit.

Find: The new temperature in FahrenheitFind: The new temperature in Fahrenheit

Solution:Solution: 1 C1 Coo = 1.8 F = 1.8 Foo

4 x 1 C4 x 1 Coo = 4 x 1.8 F = 4 x 1.8 Foo

4 C4 Coo = 7.2 F = 7.2 Foo

68 68 ooF – 7.2 FF – 7.2 Foo = 60.8 = 60.8 ooFF

http://www.hazelwood.k12.mo.us/~grichert/sciweb/thermo.htm

Thermocouple thermometersThermocouple thermometers

Used where a normal thermometer Used where a normal thermometer cant be usedcant be used

Furnaces, boilers, and nuclear Furnaces, boilers, and nuclear reactorsreactors

Allows us to read the temperature far Allows us to read the temperature far away from the actual measuring pointaway from the actual measuring point

How does a thermocouple thermometer How does a thermocouple thermometer work?work?

Temperature measuring device that Temperature measuring device that depends on changes in electrical depends on changes in electrical

properties of certain metalsproperties of certain metals

When two specific metals are joined When two specific metals are joined together a small voltage develops together a small voltage develops across the connecting joint when across the connecting joint when

opposite ends are at different opposite ends are at different temperaturestemperatures

How does a thermocouple thermometer How does a thermocouple thermometer work?work?

Metals: Iron and constantan or Metals: Iron and constantan or chromel and constantanchromel and constantan

Voltage is very lowVoltage is very low Few microvolts or millivoltsFew microvolts or millivolts

Increasing the temperature difference Increasing the temperature difference increases the voltageincreases the voltage

Thermocouple thermometersThermocouple thermometers

Formed by using two thermocouple Formed by using two thermocouple junctionsjunctions

Thermocouple thermometersThermocouple thermometers

Used to measure the temperature Used to measure the temperature difference between a known temperature difference between a known temperature

(T(TRR) and an unknown temperature (T)) and an unknown temperature (T)

Thermocouple thermometersThermocouple thermometers

The two junctions produce separate The two junctions produce separate voltages that oppose one othervoltages that oppose one other

If the voltages are equal, the If the voltages are equal, the voltmeter will read zero and the voltmeter will read zero and the

temperatures are the sametemperatures are the same

If T is greater than TIf T is greater than TRR it produces a it produces a positive voltagepositive voltage

If T is less than TIf T is less than TRR it produces a it produces a negative voltagenegative voltage

Thermocouple thermometersThermocouple thermometers

Reference junction is usually placed in Reference junction is usually placed in an icy-water mixture with a known an icy-water mixture with a known

temperature of 0temperature of 0ooCC