introduction to thermodynamics

THERMODYNAMICSTHERMO

DYNAMICS

TEMPERATURE AND THERMAL ENERGY


Thermal energy ndash a form of kinetic energy characterized by randomness of motion at the atomic and molecular level


Temperature ndash the degree or intensity of heat present in a substance or object the measure of the hotness or coldness of a body


Heat ndash the energy transit from a body of higher temperature to one of lower temperature under the influence of the variation in temperature quantity of thermal energy absorbed or given off by a body


LETrsquoS DO THISLETrsquoS DO THIS

Materials

1 beaker half filled with hot water1 beaker filled with hot water up to the brim2 ice cubesStopwatch

Materials


Procedure

Drop the cubes to the individual beakersSee what happens (Observe the rate by which the ice cube melts)

Procedure


QUESTIONShellipQUESTIONShellip

1 Which of the 2 beakers has thermal energy1 Which of the 2 beakers has thermal energy

2 Which of the 2 beakers has greater temperature


3 Which of the 2 beakers contains more heat3 Which of the 2 beakers contains more heat

ANSWERShellipANSWERShellip

1 Both fluids inside the beaker have thermal energy


2 Both have the same temperature2 Both have the same temperature

3 The beaker filled with hot water up to the brim contains greater heat


MEASURING TEMPERATUREMEASURING TEMPERATURE

1 Using the tactile sense1 Using the tactile sense

2 Using a thermometer2 Using a thermometer

PARTS OF A THERMOMETERPARTS OF A THERMOMETER

a Thermal sensora Thermal sensor

b Calibrations ~ degF degC or Kb Calibrations ~ degF degC or K

TYPES OF THERMOMETERTYPES OF THERMOMETER

1 Dial thermometer ndash aka Rotary thermometer1 Dial thermometer ndash aka Rotary thermometer1 Dial thermometer ndash aka Rotary thermometer1 Dial thermometer ndash aka Rotary thermometer

2 Glass thermometer ndash aka liquid-in-glass ~2 Glass thermometer ndash aka liquid-in-glass ~ Mercury or Colored alcoholMercury or Colored alcohol


3 Thermocouple ndash aka electronic thermometer 3 Thermocouple ndash aka electronic thermometer 3 Thermocouple ndash aka electronic thermometer 3 Thermocouple ndash aka electronic thermometer

4 Liquid crystal thermometer4 Liquid crystal thermometer4 Liquid crystal thermometer4 Liquid crystal thermometer

TEMPERATURE SCALESTEMPERATURE SCALES

11 Fahrenheit ScaleFahrenheit Scale ndash (named after Ger ndash (named after Ger physicist physicist Gabriel Daniel FahrenheitGabriel Daniel Fahrenheit) based ) based on the freezing and boiling point of water at on the freezing and boiling point of water at normal atmospheric pressure ~ 32normal atmospheric pressure ~ 32ordmF - ordmF - freezing pt and 212ordmF ndash boiling ptfreezing pt and 212ordmF ndash boiling pt

2 Celsius Scale2 Celsius Scale ndash (named after Swed ndash (named after Swed astronomer astronomer Anders C CelsiusAnders C Celsius) based on the ) based on the freezing and boiling point of water at freezing and boiling point of water at normal atmospheric pressure ~ 0normal atmospheric pressure ~ 0ordmC - ordmC - freezing pt and 100ordmC ndash boiling ptfreezing pt and 100ordmC ndash boiling pt

3 Kelvin Scale3 Kelvin Scale ndash (named after Brit physicist ndash (named after Brit physicist William T KelvinWilliam T Kelvin) erased the arbitrary ) erased the arbitrary assigned reference points thus called not a assigned reference points thus called not a relative scalerelative scale but an but an Absolute temperature Absolute temperature scalescale 0 0 = nothing ndash = nothing ndash Absolute ZeroAbsolute Zero ~ lowest ~ lowest temperature possible occurring when all temperature possible occurring when all random motion of molecules has ceased In random motion of molecules has ceased In this scale 273K ndash freezing pt of water this scale 273K ndash freezing pt of water 373K ndash boiling pt373K ndash boiling pt

CONVERSIONSCONVERSIONS

bull From degF to degC (degF -32)59

bull From degC to degF (degC 95) + 32

bull From degC to KdegC + 273

bull From degF to K(degF-32)59 + 273





It is easier to open a tight bottle cap by exposing it to heat


THERMAL EXPANSIONTHERMAL EXPANSION

EXPANSION OF MATERIALSEXPANSION OF MATERIALS

ldquoMaterials expand as their thermal energy increasesrdquo rarr Thermal

expansion


expansion

ldquoMaterials contract as their thermal energy decreasesrdquo


EXPANSION OF MATERIALS UNDER 100degCEXPANSION OF MATERIALS UNDER 100degC

Materials Materials

(1 m in length)(1 m in length)

Length of Length of ExpansionExpansion

Invar (alloy of Fe and Ni)Invar (alloy of Fe and Ni) 01 mm01 mm

Pyrex Pyrex 03 mm03 mm

Platinum alloyPlatinum alloy 09 mm09 mm

GlassGlass 09 mm09 mm

ConcreteConcrete 10 mm10 mm

SteelSteel 10 mm10 mm

BrassBrass 20 mm20 mm

AluminumAluminum 30 mm30 mm

ldquoModern bridges are usually constructed withldquoModern bridges are usually constructed with

a One end attached while the other end rests on rollers


b With tooth like seams called expansion joints


THERMOSTATTHERMOSTAT

ldquoThe amount of expansion of a material depends on the change in temperaturerdquoldquoThe amount of expansion of a material depends on the change in temperaturerdquo

The device that regulates the temperature of a material is called a thermostat It is usually consists of bimetallic strips eg Brass (alloy of Cu and Zn) and Fe that are welded together When the Brass side is heated it expands and contracts when cooled rarr can help turn onoff a device such as heaters


HEAT TRANSFERHEAT TRANSFER

The study of the flow of heat within an object or from one medium to another due to their variation in temperature


1 Radiation - energy is emitted in the form of electromagnetic waves or subatomic particles eg heatwarmth felt from a flame or bonfire sans touching it the heat from the microwave oven and the heat from the sun


METHODS OF HEAT TRANSFER METHODS OF HEAT TRANSFER

2 Conduction - heat energy transfer caused by direct contact wherein heat travels from one molecule to another For example exposing metal to a flame allowing an article to rest on a warm or hot object


ldquoHeat flows from a region of high concentration to a region of low concentrationrdquo


Hot rarr ColdHot rarr Cold

LegendLegend

3 Convection - transference of mass or heat within a fluid caused by the tendency of warmer and less dense material to rise producing air or fluid currents


Hot air risesHot air rises Air cools down becomes denseAir cools down becomes dense

Cold air sinksCold air sinksAir heats up and becomes less

dense

Air heats up and becomes less

dense

SPECIFIC HEATSPECIFIC HEAT

The amount of energy required to raise the temperature of one kilogram (1 kg) of a substance by one degC (1degC) or one Kelvin (1 K) It is expressed in terms of Joules per kilogram-Kelvin (JkgmiddotK) or Joules per kilogram degree Celsius (JkgmiddotdegC) or calorie per gram degree Celcius (calgmiddotdegC) in which 1 cal = 4186 J


THERMAL CAPACITYTHERMAL CAPACITY

The amount of heat required to raise the temperature of a substance by 1 degree (1deg) and is the product of its mass and specific heat


ΔQ = mCΔTΔQ = mCΔT

Wherein ΔQ is change in heat expressed in terms of Jm is the mass of the substance in kgC is the specific heat in JkgmiddotKΔT is the change in heat in K


WORD PROBLEMSWORD PROBLEMS

1 How much heat is needed to raise the temperature of 150 kg of water to 323 K1 How much heat is needed to raise the temperature of 150 kg of water to 323 K

2 What is the temperature of the mixture of 075 kg of water at 98degC is added to 05kg of water at 25degC in a polystyrene cup


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MEASURING TEMPERATURE

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THERMAL EXPANSION

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Materials


Materials


Procedure


Procedure











































expansion


expansion




Materials Materials































LegendLegend





dense


dense














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THERMAL EXPANSION

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expansion


expansion




Materials Materials































LegendLegend





dense


dense














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THERMAL EXPANSION

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Materials Materials































LegendLegend





dense


dense














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THERMAL EXPANSION

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LegendLegend





dense


dense














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THERMAL EXPANSION

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dense


dense














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THERMAL EXPANSION

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THERMAL EXPANSION

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THERMAL EXPANSION

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introduction to thermodynamics

Business

thermal energy thermal

heat ink

heat flows

flow of heat

greater heat

thermal expansion

lower temperature

measuring temperature