PHYSICS 3 FIS 0334

PHYSICS 3FIS 0124/0334Chapter 1Temperature and HeatSEGi education groupSEGi education groupChapter 1Concept of Thermal Expansion (For Solid and Liquid)Linear ExpansionVolume ExpansionCoefficient of ExpansionThermal Expansion of Water

SEGi education groupLearning OutcomesBy the end of this chapter, students will be able to do the following:Understand the concept of thermal expansion.Expresses the relationship of linear expansion (as well as volume expansion) in an equation in term of relative coefficient of expansion.Calculate the amount of expansion using derived equation.Explain the unusual behaviour of thermal expansion for water.SEGi education groupIntroductionHow to open this bottle without a bottle opener?

SEGi education groupIntroductionBy scissors?By spoon?

SEGi education groupIntroduction By Thermal Expansion Method

By running the flame of lighter around the cap of bottle.

By running hot water over the cap of bottle.

This will make opening easier than just simply trying to open the lid off.

This is due to thermal expansion effect of metal lid after heat added.SEGi education groupThermal ExpansionMost materials expands when their temperature increase Example: Rising temperature make the mercury expands in a laboratory thermometer as well as bend of bimetallic strips in bimetallic thermometer.

Expansion due to variation in temperature usually occurs in three forms;Linear Expansion causes increase in length (for solid)Area Expansion causes increase in surface area (for solid)Volume Expansion causes increase in volume (for solid and liquid)

SEGi education groupLinear ExpansionA rod of material has length, L at initial temperature, T. After the temperature changes by T, the length changes by L.

TT + TT + 2TLL2LTT + TT + TTLL2L2L

where is the coefficient of linear expansionSEGi education groupArea Expansion & Volume ExpansionSame case for surface area and volume of the object.

LL

As temperature increase, the length of each side increases to

where is the coefficient of area expansion = 2

SEGi education groupComparison of Linear, Area and Volume ExpansionThermal ExpansionEquationCoefficient of Expansion LinearAreaVolume

SEGi education groupAverage Coefficients of Expansion for Some Materials Near Room Temperature

SEGi education groupExample 1 - How Thermal Expansion Affects The Choice of GlasswareIf hot liquid is poured into a cold container made of ordinary glass, the container may well break due to thermal stress.(The inside surface of the glass becomes hot and expands while the outside surface is at room temperature, and the ordinary glass may not withstand the difference in expansion)

But, what about if now hot liquid is poured into container made of Pyrex glass?Pyrex glass has coefficient of linear expansion of about one-third that of ordinary glass, so the thermal stress are relatively smaller.

The expansion and contraction of materials due to changes in temperature create stresses and strains, which sometimes sufficient to cause fracturing.

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The figure shows eight square tiles that are arranged to form a square pattern with a hold in the center. If the tiles are heated, what happens to the size of the hole?The thermal expansion of the hole and the surrounding material is analogous to a photographic enlargement, in both situations everything is enlarged, including holes.Example 2 - The Expansion of HoleExample: Think of atoms as outlining a cubical hole. When the object expands, the atoms move apart and the hole increases in size.SEGi education groupQuestion 1 Why would silver and brass probably not be a good choice of metals for bimetallic strip application? (leaving aside the cost for both metals). Given that

SEGi education groupQuestion 2One way to loosen the metal lid on a glass jar is to run it under hot water. How does that work?(Hint: Compare the thermal expansion coefficient for both metal lid and glass jar)SEGi education groupQuestion 3 Linear ExpansionA steel railroad track has a length of 30.000m when the temperature is 0C. What is its length on a hot day when the temperature is 40C? Given that

SEGi education groupQuestion 4 Volume ExpansionA hollow copper cylinder is filled to the brim with water at 20.0C. If the water and the container are heated to a temperature of 91C, what is the amount of water that spills over the top of the container? Given that

SEGi education group0.011V. 17Unusual Thermal Expansion of WaterObject will expand with increasing temperature.But, water is an exception to this rule over small temperature range.

SEGi education groupUnusual Thermal Expansion of WaterWhen ice at about -4C is heated, it expands slightly up to 0C.(At 0C, phase transition occurs from ice to water)When this water is further heated, it contracts from 0C to 4C, which is unusual.Above 4C, it expands, behaving like other liquids. The density is the mass per unit of volume of a substance, so when volume changes, density changes as well.Since water contracts from 0C to 4C, its volume decreases and the density increases.Water has the minimum volume and maximum density at 4C.

SEGi education groupQuestion 5How do fish survive in icy water?

SEGi education groupUnusual Thermal Expansion of WaterThis unusual behavior of water has an important effect on plant and animal life in lakes. A lake cools from the surface down;Above 4C, the cooled water at the surface sinks to the bottom because of its greater density.But when the surface temperature drops below 4C, the water near the surface is less dense than the warmer water below.Thus, the downward flow stops and the water near the surface remain colder than the bottom, eventually freezes to become ice.The ice continues to build up on surface while water near bottom remains at 4C.The ice formation turns to be an insulating layer that prevent heat lost from underneath, offer thermal protection for marine life.SEGi education groupReferences[1] Young, H., and Freedman, R. (2014). Sears and Zemanskys university physics with modern physics: Technology update (13th ed., Pearson new international ed.). Harlow, Essex: Pearson Education.[2] Serway, R., and Vuille, C. (2007). Essentials of college physics (International student ed.). Belmont, Calif.: Thomson Brooks/Cole.[3] Cengel, Y. (1997). Introduction to thermodynamics and heat transfer (International ed.). New York: McGraw-Hill.[4] Giambattista, A., Richardson, B., and Richardson, R. (2007). College physics (2nd ed.). New York: McGraw-Hill Higher Education.

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