president universityerwin sitompulthermal physics 1/1 lecture 1 thermal physics dr.-ing. erwin...

President University Erwin Sitompul Thermal Physics 1/1

Lecture 1Thermal Physics

Dr.-Ing. Erwin SitompulPresident University

http://zitompul.wordpress.com

2 0 1 4


Textbook:“Fundamentals of Physics”, Halliday, Resnick, Walker, John Wiley & Sons, 8th Extended, 2008.

Syllabus: Chapter 18: First Law of ThermodynamicsChapter 19: Kinetic TheoryChapter 20: Second Law of Thermodynamics

Textbook and SyllabusThermal Physics


Grade PolicyThermal Physics

Final Grade = 10% Homework + 20% Quizzes + 30% Midterm Exam + 40% Final Exam + Extra Points

Homeworks will be given in fairly regular basis. The average of homework grades contributes 10% of final grade.

Written homeworks are to be submitted on A4 papers, otherwise they will not be graded.

Homeworks must be submitted on time, one day before the next lecture. Late submission will be penalized by point deduction of –10·n, where n is the total number of lateness made.

There will be 3 quizzes. Only the best 2 will be counted. The average of quiz grades contributes 20% of final grade.

The maximum lateness in coming to class is 25 minutes, otherwise attendance will not be counted.


Grade Policy Midterm and final exams follow the schedule released by AAB

(Academic Administration Bureau). Make up of quizzes must be requested within one week after the

schedule of the respective quiz. Make up for mid exam and final exam must be requested directly

to AAB.

●Heading of Written Homework Papers (Required)

Thermal PhysicsHomework 2

Emelie Raturandang0029202400058

21 March 2027

No.1. Answer: . . . . . . . .

Thermal Physics


Grade Policy In order to maintain the integrity, the maximum score of a make

up quiz or exam, upon discretion, can be set to 90. Extra points will be given if you solve a problem in front of the

class. You will earn 1 or 2. Lecture slides can be copied during class session. It is also

available on internet. Please check the course homepage regularly.

http://zitompul.wordpress.com

The use of internet for any purpose during class sessions is strictly forbidden.

Thermal Physics


Chapter 18

First Law of Thermodynamics

Thermal Physics


Thermodynamics and EngineeringChapter 18 First Law of Thermodynamics

One of the principal branches of physics that is closely related to Engineering is thermodynamics.

Thermodynamics is the study of thermal energy and its applications. The main concern is heat and temperature, and their relation to energy and work.

Some relations between thermodynamics and engineering are: Automobile engineers are concerned with the heating of a car

engine and the effect of temperature to engine efficiency. Building physics engineers are concerned with the

temperature control inside a building. Process engineers are concerned with the cooling or heating of

the material in the production lines. Medical engineers are concerned with how a patient’s

temperature might distinguish between a viral infection or a cancerous growth.

Electrical engineers are concerned on how to design appliances and electronic devices which can work without overheating problems.

Electrical Engineering students are concerned on how to pass the Thermal Physics class with good grade....


TemperatureChapter 18 First Law of Thermodynamics

The starting point in discussion of thermodynamics is the concept of temperature and how it is measured.

As one of the seven SI base quantities, temperature is measured on the Kelvin scale. The unit is called kelvins, with the notation K.

The temperature of a body has no upper limit, but it does have a lower limit, the absolute zero temperature, 0 kelvins or 0 K.


The Zeroth Law of Thermodynamics The properties of many bodies change as we alter their

temperature. For example, as their temperature increases, the volume of a

liquid increases, the length of a metal rod increases, the electrical resistance of a wire increases, the pressure exerted by a confined gas increases.

We can use any one of these properties as the basis of an instrument that will help us pin down the concept of temperature.

Assume that we have a thermoscope, an instrument with digital display that will display increasing number if it is heated or decreasing number if it is cooled.

Chapter 18 First Law of Thermodynamics


The Zeroth Law of Thermodynamics We now put the thermoscope (body T) into

intimate contact with another body (body A). The entire system is confined within a thick-

walled insulating box. We let body T and body A be in thermal

equilibrium, where the value indicated by the thermoscope does not change anymore.

Next, we put body T into intimate contact with another body B. We let the two bodies come to thermal equilibrium at the same reading of the thermoscope.

The question: If we put bodies A and B into intimate contact, are they immediately in thermal equilibrium with each other?

Zeroth Law of Thermodynamics:“If bodies A and B are each in themal equilibrium with a third body T, then A and B are in thermal equilibrium with each other.”



Measuring TemperatureChapter 18 First Law of Thermodynamics

The Triple Point of Water To set up a temperature scale, we pick some

reproducible thermal phenomenon as a standard fixed point and assign a certain Kelvin temperature to its environment.

For technical reasons, the triple point of water is selected. At this condition, liquid water, solid ice, and water vapor coexist, at a certain value of pressure and temperature.

By international convention, the triple point of water has been assigned a value of 273.16 K.

3 273.16 KT ?Isn’t it supposed to be 273.15 K?



The Constant-Volume Gas Thermometer The standard thermometer is based on the

pressure of a gas in a fixed volume. As shown on the next figure, the thermometer

consists of a gas-filled bulb connected by a tube to a mercury manometer.

By raising and lowering reservoir R, the mercury level in the left arm of the U-tube can always be brought to the zero of the scale to keep the gas volume constant.

The temperature of any body in thermal contact with the bulb is then defined to be:

T Cp C : a constantp : the pressure exerted by the gas

The pressure p is given by:

0p p gh p0 : the atmospheric pressureρ : the density of mercuryh : the difference between the mercury levels



If we now put the bulb in a liquid with triple-point temperature, the temperature now being measured is:

3 3T Cp

With this thermometer, different gases in the bulb give slightly different results.

However, as we use smaller and smaller amounts of gas (decreasing p3), the reading converge nicely to a single temperature.

33

pT T

p

After eliminating C, the temperature can be given as:

3

(273.16)p

p


The Celsius and Fahrenheit ScalesChapter 18 First Law of Thermodynamics

In the Celsius scale (formerly called the centigrade scale), the temperatures are measured in degrees, and the Celsius degree has the same size as the kelvin.

The zero of the Celsius scale is shifted to a more convenient value than absolute zero.

C 273.15T T

The Fahrenheit scale employs a smaller degree than the Celsius scale and a different zero of temperature.

F C

932

5T T


CheckpointChapter 18 First Law of Thermodynamics

The figure here shows three linear temperature scales with the freezing and boiling points of water indicated. (a) Rank the degrees on these scales by size, greatest first. (b) Rank the following temperatures, highest first: 50°X, 50°W, and

50°Y.

(a) All tie

(b) 50°X, 50°Y, 50°W


ProblemChapter 18 First Law of Thermodynamics

Suppose you come across old scientific notes that describe a temperature scale called Z on which the boiling point of water is 65.0°Z and the freezing point is –14.0°Z. To what temperature on the Fahrenheit scale would a temperature of T = –98.0°Z correspond?

18098.0 Z 32 (84.0) F

79.0 159.4 F


Thermal ExpansionChapter 18 First Law of Thermodynamics

When the temperature of an object is raised, the body usually exhibit thermal expansion.

With the added thermal energy, the atoms can move a bit farther from one another than usual, against the spring-like interatomic forces that hold every solid together.

Such thermal expansion is a property of material. Some of which can be put to common use. Thermometers and thermostats may be based on the differences in expansion between the components of a bimetal strip (see below).

Familiar liquid-in glass thermometers are based on the fact that liquids such as mercury and alcohol expands to a different (greater) extend than their glass containers.



Linear Expansion In the temperature of a metal rod of length L is raised by an

amount ΔT, its length is found to increase by an amount:

L L T α : coefficient of linear expansion [/°C or /K]

The coefficient of linear expansion α depends on the material. It also varies with temperature. But, for most practical purposes it can be taken as constant for a certain material.



Volume Expansion If all dimensions of a solid expand with temperature, the volume of

that solid must also expand. If the temperature of a solid or liquid whose volume is V is

increased by an amount ΔT, the increase in volume is found to be:

V V T β : coefficient of volume expansion [/°C or /K]

3 ?Can you find the exact relation?

● The same steel ruler at two different temperature


CheckpointChapter 18 First Law of Thermodynamics

The figure here shows four rectangular metal plates, with sides of L, 2L, or 3L. They are all made of the same material, and their temperature is to be increased by the same amount.Rank the plates according to the expected increase in (a) their vertical heights and (b) their areas, greatest first.

(a) 2 and 3 tie, then 1, then 4

(b) 3, then 2, then 1 and 4 tie


ProblemChapter 18 First Law of Thermodynamics

On a hot day in Las Vegas, an oil trucker loaded 37 000 l of diesel fuel. It encountered cold weather on the way to Utah, where the temperature was 23.0 K lower than in Las Vegas, and where it delivered its entire load. How many liters did it deliver? The coefficient of volume expansion for diesel fuel is 9.50×10–4/°C, and the coefficient of linear expansion for its steel truck tank is 11×10–6/°C.

V V T 4(37000)(9.50 10 )( 23.0)

808.45 l

deliveredV V V 37000 808.45 36191.55 l

?Who paid for the “missing” diesel fuel?

! Although looked much, the missing fuel is only 2.2 % of the original load.


Temperature and HeatChapter 18 First Law of Thermodynamics

The temperature of a cup of hot coffee, left sitting on a table, will fall –rapidly at first but then more slowly– until it reaches room temperature The room and the coffee are then in thermal equilibrium.

Generalizing the situation, we describe the coffee as a system (with temperature TS) and the room environment as another system (with temperature TE) .

Our observation is that if TS ≠ TE, then TS will change (TE can also change some) until the two temperatures are equal and thus thermal equilibrium is reached.

Such a change in temperature is because of a transfer of energy between the system and the system’s environment. The transferred energy is called heat and is symbolized with Q.

Heat is positive when energy is absorbed by the system.

Heat is negative when energy is released or lost by the system.


Temperature and HeatChapter 18 First Law of Thermodynamics

Heat is the energy transferred between a system and its environment because of a temperature difference that exists between them.

Besides, energy can also be transferred between a system and its environment as work W via a force acting on a system.

By old definition, heat was measured in terms of its ability to raise the temperature of water.

In SI system, the calorie (cal) was defined as the amount of heat that would raise the temperature of 1 g of water from 14.5°C to 15.5°C.

In the British system, the British thermal unit (Btu) was defined as the amount of heat that would raise the temperature of 1 lb of water from 63°F to 64°F.

● 1 cal = 4.1868 Joule


Class Group AssignmentsChapter 18 First Law of Thermodynamics

1.Unsatisfied with the Celsius and Fahrenheit temperature scales, you decide to create your own. On your temperature scale, the ice point is 77M and the steam point is at 437M, where “M” stands for “my scale.” What temperature on your scale corresponds to 68F?(a) 154 °M (d) 168 °M(b) 140 °M (e) 136 °M(c) 149 °M

2.A constant-volume gas thermometer is used to measure the temperature of an object. When the thermometer is in contact with water at its triple point (273.16 K), the pressure in the thermometer is 8.950×104 Pa. When it is in contact with the object, the pressure is 7.650×104 Pa. The temperature of the object is:(a) 23 K (b) 233 K (c) 310 K (d) 314 K (e) 2636 K



3.A glass tube with the volume 200 cm3 is completely filled with mercury at 20°C. If the temperature of the system is increased to 100°C, determine the amount of mercury that overflows. The coefficient of linear expansion of glass is 0.34×10–5 K–1 while coefficient of volume expansion of mercury is 1.82×10–4 K–1.(a) 1.43 cm3 (d) 2.72 cm3

(b) 2.75 cm3 (e) 3.57 cm3

(c) 4.81 cm3

4.A brass cube, 10 cm on a side, is raised in temperature by 200°C. The coefficient of volume expansion of brass is 57 × 10–6/°C. By what percentage is any one of the 10-cm edges increased in length?(a) 4% (d) 1.14%(b) 0.38% (e) 0.29%(c) 0.17%



5.A gram of distilled water at 4°C:(a) will increase slightly in weight when heated to 6°C.(b) will decrease slightly in weight when heated to 6°C. (c) will increase slightly in volume when heated to 6°C. (d) will decrease slightly in volume when heated to 6°C.

(e) will not change in either volume or weight.


Homework 11.(18-7) Suppose that on a linear temperature scale X, water boils at

–53.5°X and freezes at –170°X. What is a temperature of 340 K on the X scale? (Approximate water’s boiling point as 373 K.)

2.(18-17) A steel rod is 3.000 cm in diameter at 25.00°C. A brass ring has an interior diameter of 2.992 cm at 25.00°C. At what common temperature will the ring just slide onto the rod? (Hint: For coefficients, use only the value given by the textbook.)


●Be sure to understand the homework problems.●Validation tests will be conducted occasionally.

Deadline: 16 April 2014.

president universityerwin sitompulthermal physics 1/1 lecture 1 thermal physics dr.-ing. erwin...

Documents