nAmiBIA UniVERSITY OF SCIEnCE AnD TECHnOLOGY

FACULTY OF HEALTH AND APPLIED SCIENCES

DEPARTMENT OF NATURAL AND APPLIED SCIENCES

QUALIFICATION: BACHELOR OF SCIENCE

QUALIFICATION CODE: 07BOSC LEVEL: 6

COURSE CODE: TPH601S COURSE NAME: THERMAL PHYSICS

SESSION: JULY 2016 PAPER: THEORY

DURATION: 3 HOURS MARKS: 100

SECOND OPPORTUNITY EXAMINATION QUESTION PAPER

EXAMINER(S) Prof. ldugba M. Echi

MODERATOR: Dr. AI-Mas Sendegeya

INSTRUCTIONS 1. Answer ALL the questions.

2. Write clearly and neatly.

3. Number the answers clearly.

PERMISSIBLE MATERIALS

Non-programmable Calculators

ATTACHMENT

None

THIS QUESTION PAPER CONSISTS OF 5 PAGES (Including this front page)

In question 1, write the letter corresponding to your choice in your answer booklet

Each question in this section carries 1 mark

QUESTION 1 [20]

1.1 Which of the following statements is/are correct : two bodies are in thermal equilibrium if I they do not exchange heat when in contact II their temperatures are equal Ill they have the same masses IV they have the same volume

A I, Ill B II, IV C I, II D II, IV (1)

1.2 The temperature of a hot cup of coffee is 158°F. What is the equivalent temperature on a Celsius scale?

A 80°C B 75°C C 70°C D 65°C (1)

1.3 The thermometric property of the constant volume gas thermometer is----A Volume changes with changes in temperature B Pressure changes with change in temperature C Pressure changes with change in volume D Pressure changes at constant temperature (1)

1.4 The mode of heat transfer in which the molecules of the medium carry the heat to a place of lower temperature is called-------

A Convention B Radiation C Conduction D Convection (1)

1.5 Heat can cause a material to change size, temperature and phase. The thermal coefficients associated with these effects respectively are: A Expansivity, specific heat capacity, specific latent heat. B Conductivity, expansivity, latent heat C Specific heat capacity, latent heat and expansivity D Specific conductivity, specific gravity, specific condensation (1)

1.6 An isolated thermodynamic system ------A allows only exchange of energy between system and the surrounding B allows exchange of energy and mass C does not allow exchange of energy and mass D does not allow exchange of mass only (1)

1.7 The first law of thermodynamics expresses the conservation of energy between -----energies.

A kinetic, heat and mechanical heat B kinetic, internal and heat c D

internal, heat and mechanical internal, kinetic and mechanical work

1.8 A gas is compressed adiabatically from a volume of 20m3 to 11m3. The change in internal

energy of the gas is

Jll

A PdV 20

B 9P C Pln(ib) 2

D J11

VdP 20

(1)

(1)

1.9 The figure below shows a P-V diagram for an adiabatic compression of 1 mole of an ideal gas. Evaluate the adiabatic constant if Cp/Cv = 1.2

P ( N m·2)

15

ｾｾＭＭＭＭＭＭｾｾＭﾷＭＭｾＩ＠ v(m3) 10 s

A 137.60 J B 237.73J C 150.00J D 157.63 J

1.10 The units of heat energy and mechanical work are:

A J and Js·2 B J and Js C J and Nm-1 D J and J

1.11 Which of the followings will give rise to a higher entropy change in a thermodynamic system?

A

B c D

Heating the system at constant temperature Heating the system with rising temperature Heating the system at constant volume Heating the system at constant pressure

1.12 The Carnot engine operates in a cycle between-------

A two isotherms and 2 adiabats B two isobars and 2 isotherms C two adiabats and 2 isobars D three isotherms and isobars

1.13 You can force a house to the stream but you can't force it to drink water, goes a popular adage. Where does this adage apply in the working of a refrigerator?

A condenser B compressor C evaporator D metering

1.14 Which of following statements is not true about the Rankine and Brayton heat engines?

A Both operate between 2 adiabats and 2 isobars B Their thermal efficiencies are the same C Brayton engine uses boiler while Rankine uses fuel combustion D Their thermal efficiency are less than that of a Carnot engine operating between

the same reservoirs.

1.15 The Sterling heat engine operates between---

A two isotherms and two adiabats B c D

two isotherms and two adiabats two isometrics and two isotherms two isotherms and two isobars

3

(1}

(1}

(1}

(1}

(1}

(1}

(1}

1.16 In a reversible thermodynamic process the entropy change of the universe is

A greater than zero B zero C less than zero D 403JK-1

1.17 If dU= dU{S,V} is an exact differential, which of the followings is not true?

A U is a thermodynamic potential. B S is a state variable c D

V is a state variable U, Sand V are state variables

1.18 Four molecules, three molecules and 2 molecules have the speeds of 10, 15, 25ms-1

respectively. The rms speed of the molecules to the nearest whole number is

(1}

{1}

A 10ms-1 B 13ms-1 C 16ms-1 D 19ms-1 {1}

1.19 The parameter which measures how far molecules move on the average before they collide is -----

A rms speed B average speed C collision frequency D mean free path {1}

1.20 Which of the following is not a thermodynamic potential of any state variables?

A Internal energy B Gibb's function C Pressure function D Enthalpy function {1}

QUESTION 2 [20]

{3} 2.1 Define the specific latent heat of evaporation of water and give the unit.

2.2 If you are required to determine the specific latent heat of fusion of ice by the method of mixture. 2.2.1 List the apparatus and materials you will use. {2} 2.2.2 List the quantities you will measure. (2} 2.2.3 Write the theory behind the experiment and show how your specific latent heat

will be obtained. (2}

2.3 A solid of mass 500g is heated in a beaker of water to a temperature of 95°C. The solid was then transferred quickly into a copper calorimeter of mass 600g containing water of mass 400g at a temperature of 30°C. The steady temperature of the mixture is 40°C. Evaluate the specific heat capacity of the solid [specific heat capacity of water= 4200 Jkg-1K-\ specific heat capacity of copper= 385 JkgK-1

] {8}

2.4 Explain very briefly what is anomalous in water expansion and why it is useful to aquatic life.

QUESTION 3

3.1

3.2

3.3

3.4

An isolated gas has some internal energy. Explain the origin of the internal energy.

Explain how the internal energy of a gas can be changed .

Explain the following processes: isobaric, isothermal and adiabatic processes.

Write the adiabatic formula for idea gas and compare it with the Boyle's law formula

4

{3}

[20]

{3}

{3}

(3}

{3}

3.5 The volume of 50g of oxygen gas is compressed isothermally at 85°C to half its original value.

Evaluate the work done on the gas [Gas constant R=8.314Jmor1K-\ molar mass of oxygen = 32g mor1

] (8)

QUESTION 4 [20]

(3)

(3)

4.1

4.2

State the Kelvin-Plank second law of thermodynamics.

Sketch the P-V diagram of a Carnot engine.

4.3 State Carnot theorem. An engine operates between two reservoirs at temperatures 120°C and 20°C. The heat input is 1250 J and the heat rejected is 1010 J. Show that this engine is

4.4

4.5

not a Carnot engine (8)

Explain the functions of the condenser and expansion valve in a refrigerator.

A refrigerator compressor may be working very well and there may be no leakage of refrigerant, yet the fridge may not cool. Explain why?

(3)

(3)

QUESTION 5 [20]

5.1 Distinguish between a reversible and irreversible thermodynamic processes given one example each. (2)

5.2 Evaluate the entropy of 600g water at 25°( [specific heat capacities of ice =2100Jkg-1K-\ water= 4200Jkg-1K-\ specific latent heat of fusion of water= 3.33x105Jkg-1

] (6)

5.3 A thermodynamic potential U is given by ｕＨｓＬｖＩ］ｾ＠ v-213e1-s, where ｾ｡ｮ､＠ A are constants.

5.3.1 Obtain the differential of U (4)

5.5.2 Hence verify Maxwell relation. (4)

5.4 The molar mass of C02 gas is 4.4x10-2kgmor1• Find the Vrms of the molecules of the gas at

27°C. (4)

********** GOODLUCK **********

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