Quiz Samples for Chapter 18 General Physics I Name ...kpope.korea.ac.kr/GenPhy/Quiz/CH-18-Exercise-2020-General-Physics… · Quiz Samples for Chapter 18 Temperature, Heat, and the

General Physics IQuiz Samples for Chapter 18

Temperature, Heat, and the First Law of ThermodynamicsJune 1, 2020

Name: Department: Student ID #:

Notice

� +2 (−1) points per correct (incorrect) answer.

� No penalty for an unanswered question.

� Fill the blank ( ) with � (8) if the statement iscorrect (incorrect).

� Textbook: Walker, Halliday, Resnick, Principlesof Physics, Tenth Edition, John Wiley & Sons(2014).

18-1 Temperature

1. (�) Physicists measure temperature on the Kelvinscale, which is marked in units called kelvins.

2. (�) Although the temperature of a body has noupper limit, it does have a lower limit, the zerokelvin (0 K).

3. (�) The Zeroth Law of Thermodynamics:If bodies A and B are each in thermal equilibriumwith a third body T , then A and B are in thermalequilibrium with each other.

4. (�) When two gases separated by a diathermalwall are in thermal equilibrium with each otheronly their temperatures must be the same.

5. The Triple-Point of Water:

(a) (�) In a triple-point cell, solid ice, liquidwater, and water vapor coexist in thermalequilibrium.

(b) (�) Liquid water, solid ice, and water vapor(gaseous water) can coexist, in thermalequilibrium, at only one set of values ofpressure and temperature.

(c) (�) The triple point of water has beenassigned a value of

T3 = 273.16 K

as the standard fixed-point temperature forthe calibration of thermometers.

(d) (�) We do not use a degree mark in reportingKelvin temperatures. It is 300 K (not 300◦K),and it is read “300 kelvins” (not “300 degreesKelvin”).

(e) (�) The usual SI prefixes apply. Thus, 0.0035K is 3.5 mK.

(f) (�) The unit of a temperature difference isalso K.

6. The Constant-Volume Gas Thermometer:

(a) (�) It consists of a gas-filled bulb connectedby a tube to a mercury manometer.

(b) (�) The temperature of anybody in thermalcontact with the bulb is

T = Cp,

where C is a constant and p is the pressure ofthe gas.

(c) (�) Temperature T

T = T3p

p3,

where p3 is the pressure measured at thetriple-point of water T3 = 273.16 K.

(d) (�) Constant-volume gas thermometers usingdifferent gases all indicate nearly the sametemperature when in contact with the sameobject if the particle concentrations are allextremely small.

18-2 The Celsius and Fahrenheit Scales

1. (a) (�) The Celsius temperature scale is definedby

TC = T − 273.15◦,

with T in kelvins.

(b) (�) The Fahrenheit temperature scale isdefined by

TF =9

5TC + 32◦.

©2020 KPOPEEE All rights reserved. Korea University Page 1 of 6



(c) (�) We use the letters C and F to distinguishmeasurements and degrees on the two scales.Thus,

0◦C = 32◦F

means that 0◦ on the Celsius scale measuresthe same temperature as 32◦ on theFahrenheit scale.

(d) (�) A temperature difference of 5 Celsiusdegrees (note the degree symbol appearsafter C) is equivalent to a temperaturedifference of 9 Fahrenheit degrees,

5C◦ = 9F◦.

(e) (�) Fahrenheit and Kelvin scales agreenumerically at a reading of

574.5875◦F = 574.5875 K = 301.4375◦C.

(f) (�) Fahrenheit and Celcius scales agreenumerically at a reading of

−40.0◦F = −40.0◦C = 233.15 K.

(g) (�) 0◦C is the same as

0◦C = 32◦F = 273.15 K.

(h) (�) 20◦C is the same as

20◦C = 68◦F = 293.15 K.

(i) (�) 100◦C is the same as

100◦C = 212◦F = 373.15 K.

18-3 Thermal Expansion

1. Examples of Thermal Expansion:

(a) (�) You can often loosen a tight metal jar lidby holding it under a stream of hot water.

(b) (�) Sections of the bridge are separated byexpansion slots so that the sections have roomto expand on hot days without the bridgebuckling.

(c) (�) When a Concorde flew faster than thespeed of sound, thermal expansion due to therubbing by passing air increased the aircraft’slength by about 12.5 cm.

(d) (�) When a dental cavity is filled, the fillingmaterial must have the same thermalexpansion properties as the surroundingtooth. Otherwise, consuming cold ice creamand then hot coffee would be very painful.

(e) (�) Thermometers and thermostats may bebased on the differences in expansion betweenthe components of a bimetal strip.

2. (a) (�) If the temperature of a metal rod oflength L is raised by an amount ∆T , itslength is found to increase by an amount

∆L = Lα∆T,

where α is a constant called the coefficientof linear expansion. The correspondingunit is 1/C◦ or K−1.

(b) (�) If the temperature of a solid or liquidwhose volume is V is increased by an amount∆T , the increase in volume is found to be

∆V = V β∆T,

where β is a constant called the coefficientof volume expansion and is approximatelythree times of the coefficient of linearexpansion,

β ≈ 3α.

The corresponding unit is 1/C◦ or K−1.

(c) (�) The coefficient of areal expansion is 2α.The corresponding unit is 1/C◦ or K−1.

3. When the temperature of a copper penny isincreased by 100 C◦, its diameter increases by0.17 %.

(a) (�) The area of one of its faces increases byabout 0.34 %.

(b) (�) The volume of the penny is increases byabout 0.51 %.

18-4 Absorption of Heat

1. (�) The thermal energy of an object is associatedwith the random motions of its molecules.




2. (�) Heat Q is energy that is transferred between asystem and its environment because of atemperature difference between them. It can bemeasured in joules (J), calories (cal), or kilocalories(Cal or kcal) with

1 cal = 4.1868 J.

3. (�) If heat Q is absorbed by an object, the object’stemperature change Tf − Ti is related to Q by

Q = C(Tf − Ti),

where C is the heat capacity of the object. Theunit of the heat capacity is

cal/K or J/K.

4. (�) The heat capacity of an object is

C = cm,

where c is the specific heat and m is the mass ofthe object. The unit of the specific heat is

cal

g ·Kor

J

kg ·K.

5. (�) The heat capacity of an object is the amountof heat energy to raise its temperature by 1K(◦C).

6. (�) Two different samples have the same mass andtemperature. Equal quantities of energy areabsorbed as heat by each. Their final temperaturesmay be different because the samples have differentspecific heats.

7. (�) The molar specific heat of a material is theheat capacity per mole, which means per6.022 140 76 × 1023 elementary units of thematerial. The unit of the molar specific heat is

J

mol ·K.

8. (�) The amount of energy required per unit massto change the state (but not the temperature) of aparticular material is its heat of transformationL. Thus,

Q = Lm.

9. (�) A heat of transformation of a substance is theenergy per unit mass absorbed as heat during aphase transformation.

10. (�) The three phases of matter are solid, liquid,and gas.

11. (�) The heat of vaporization LV is the amountof energy per unit mass that must be added tovaporize a liquid or that must be removed tocondense a gas. For water,

LV = 539 cal/g = 40.7 kJ/mol = 2256 kJ/kg.

12. (�) The heat of fusion LF is the amount ofenergy per unit mass that must be added to melt asolid or that must be removed to freeze a liquid.For water,

LF = 79.5 cal/g = 6.01 kJ/mol = 333 kJ/kg.

13. Object A, with heat capacity CA and initially attemperature TA, is placed in thermal contact withobject B, with heat capacity CB and initially attemperature TB. The combination is thermallyisolated. If the heat capacities are independent ofthe temperature and no phase changes occur, thefinal temperature of both objects is T .

(a) (�) The energy conservation leads to theconstraint

CA(TA − T ) = CB(T − TB).

(b) (�) The final temperature T is

T =CATA + CBTBCA + CB

.

14. Solid A, with mass M , is at its melting point TA.It is placed in thermal contact with solid B, withheat capacity CB and initially at a temperatureTB(TB > TA). The combination is thermallyisolated. A has a latent heat of fusion L and whenit has melted has heat capacity CA. If Acompletely melts the final temperature of both Aand B is T .




(a) (�) The energy conservation leads to theconstraint

CA(T − TA) +ML = CB(TB − T ).

(b) (�) The final temperature T is

T =CATA + CBTB −ML

CA + CB.

18-5 The First Law of Thermodynamics

1. (�)

Insulator

Piston

Thermal reservoir

A cylinder of cross section A is filled with a gas ofpressure p. The force on the lid is F = pA and dsis the displacement of the lid. The differential workdW done by the gas during the displacement is

dW = F · ds = (pA)(ds) = p(Ads) = pdV,

where dV is the differential change in the volumeof the gas.

2. (a) (�)

Gas moves from i to f, doing positive work.

W =

∫dW =

∫ Vf

Vi

pdV.

(b) (�) The work W done by the gas depends onthe path i→ f . For given Vi and Vf , W is notunique.

(c) (�) The gas does work in the process i→ a.In the process a→ f , the gas does not workbecause dV = 0.

(d) (�) If the path is reversed, thenWf→i = −Wi→f < 0, the gas does negativework.

(e) (�) Cycling clockwise path on the p-V plotyields a positive net work.

3. The First Law of Thermodynamics: Let Qand W be the heat supplied to the gas and workdone by the gas.

(a) (�) Q−W is the change of the internalenergy of the gas

∆Einternal = Einternal,f − Einternal,i = Q−W.

(b) (�) If the thermodynamic system undergoesonly a differential change, we can write thefirst law as

dEinternal = dQ− dW = dQ− pdV.

4. Some Special Cases of the First Law ofThermodynamics:

(a) (�) Adiabatic Processes: It occurs sorapidly or occurs in a system that is so wellinsulated that no transfer of energy as heatoccurs between the system and itsenvironment.

Q = 0 → ∆Einternal = −W.

(b) (�) Constant-Volume Processes:

∆V = 0 → W = 0 → ∆Einternal = Q.




(c) (�) Cyclical Processes: The system isrestored to its initial state.

∆Einternal = 0 → Q = W.

(d) (�) Free Expansions: These are adiabaticprocesses in which no transfer of heat occursbetween the system and its environment andno work is done on or by the system. Thus,

Q = W = ∆Einternal = 0.

18-6 Heat Transfer Mechanisms

1. Conduction:

Hot reservoir Cold reservoir

(a) (�) The heat Q transfers steadily byconduction from the hot reservoir oftemperature TH to the cold reservoir oftemperature TC that are connected by auniform material of cross section A and lengthL as

dQ

dt∝ ATH − TC

L,

where t is the time elapsed.

(b) (�) The conduction rate Pconduction is theamount of energy transfer per unit time as,

Pconduction =dQ

dt= kA

TH − TCL

,

where k is the thermal conductivity of amaterial.

(c) (�) The thermal resistance R to conduction isdefined by

R =L

k.

A high R-value is a poor thermal conductorand thus a good thermal insulator.

2. Conduction Through a Composite Slab:Heat is transferred at a steady rate through acomposite slab made up of two different materialswith different thicknesses L1 and L2 and differentthermal conductivities k1 and k2, respectively. Thetemperatures of the hot reservoir are TH and thatof the cold reservoir is TC . Both slabs are ofcommon cross section A. The steady-statetemperature at the interface of the two materials isTX . Material 1 (2) is attached to the cold (hot)reservoir.

Hot reservoir Cold reservoir

(a) (�) Because the heat is transferred at asteady rate,

k2ATH − TX

L2= Pconduction = k1A

TX − TCL1

.

(b) (�) The interface temperature TX yields

TX =k1L2TC + k2L1THk1L2 + k2L1

.

(c) (�) Pconduction can be expressed as

Pconduction = kATH − TC

L,

where L = L1 + L2 and

1

k=

1

L

(L1

k1+L2

k2

).




3. (�)Convection occurs when temperaturedifferences cause an energy transfer by motionwithin a fluid.

4. Radiation is an energy transfer via the emissionof electromagnetic energy.

(a) (�) The rate Pradiation at which an object oftemperature T emits energy via thermalradiation is

Pradiation = σεAT 4,

where σ is the Stefan-Boltzmann constant, εis the emissivity of the object’s surface, A is

its surface area, and T is its surfacetemperature (in kelvins).

(b) (�) The rate Pabsorption at which an objectabsorbs energy via thermal radiation from itsenvironment, which is at the uniformtemperature Tenvironment (in kelvins), is

Pabsorption = σεAT 4environment.

(c) (�) The net rate Pnet of energy exchange dueto thermal radiation is

Pnet = Pabsorption − Pradiation

= σεA(T 4environment − T 4).


Documents

Quiz Samples for Chapter 18 General Physics I Name ...kpope.korea.ac.kr/GenPhy/Quiz/CH-18-Exercise-2020-General-Physics… · Quiz Samples for Chapter 18 Temperature, Heat, and the