Presentation Fzk

8/7/2019 Presentation Fzk

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Heat capacity

D E FIN IT IO N O F H E A T C A PA

E xa m p le o f q u e stio n

E Q U A T IO N

H e a t ca p a city fo r certa in su b s

u

id is d e fin e d a s th e h e a t re q u ire d to ra ise u n it m a ss of su b sta n ce b y o n e d e g r


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Heat capacity

E Q U A T IO N


D E FIN IT IO N O F H EA T C A PA C


= ,Q H ea t su p p lied to sub stan ce= ,m M a ss o f th e su b sta n c e= ,c S p e cific h e a t ca p a city

= .T Te m pe ra tu re rise


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Heat capacity




E Q U A T IO N

Specific Heat Capacities of Some

Substances[C (J K-1 g-1 or J oC-1 g-1)]aluminiu

mC = 0.90 water C= 4.18

carbon C = 0.72 ethanol

(ethylalcohol)

C = 2.44

copper C = 0.39 sulfuricacid(liquid)

C = 1.42

lead C = 0.13 sodium

chloridesolid

C = 0.85

mercury C = 0.14 potassiumhydroxidesolid

C = 1.18


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Heat capacity

.E xa m p le o f q u e stion

E Q U A T IO N


H e a t ca p a city fo r ce rta in su b s

d

to in cre a se th e te m p e ra tu re o f 2 5 0 g o f w ater fro m 2 0 o

C to 5 6 o

. =C q m x C x


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Temperature is ameasure of theaverage amount ofkinetic energypossessed by theparticles in a sampleof matter. The morethe particles vibrate,translate and rotate,the greater thetemperature of theobject.

It is the temperaturedifference betweenthe two neighboringobjects that causesthis heat transfer. The heat transfercontinues until the

two objects havereached thermal

H E A T T R A N S F E R

D e fin itio n o f te m p e ra tu r

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Conductive heatflow involvesthe transfer ofheat from onelocation toanother in theabsence of anymaterial flow.

There isnothing

physical ormaterialmoving fromthe hot waterto the cold

water. Onlyenergy is


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The net effect ofthese elasticcollisions is thatthere is atransfer of

kinetic energyacross theboundary to theparticles on theopposite side.

The more

energeticparticles will losea little kineticenergy and theless energeticparticles willgain a littlekinetic energy


C o n d u ctio n


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In conduction,there is no nettransfer ofphysical stuffbetween the

objects. Nothingmaterial movesacross theboundary. Thechanges intemperature are

wholly explainedas the result ofthe gains andlosses of kineticenergy duringcollisions.

Heat transfer


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Convection is theprocess ofheat transferfrom onelocation to thenext by themovement offluids.

The moving fluidcarries energywith it. Thefluid flowsfrom a hightemperaturelocation to a

lowtemperature


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Radiation is the transferof heat by means ofelectromagneticwaves. To radiatemeans to send out orspread from a central

location.

All objects radiate energyin the form ofelectromagneticwaves. The rate atwhich this energy is

released isproportional to theKelvin temperature(T) raised to thefourth power.

Radiation rate = kT4


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The energy radiated froman object is usually acollection or range ofwavelengths. This isusually referred to asan emission spectrum

Hotter objects tend to

emit shorterwavelength, higherfrequency radiation

Thermal radiation is aform of heat transferbecause theelectromagneticradiation emittedfrom the sourcecarries energy awayfrom the source tosurrounding (ordistant) objects. Thisenergy is absorbed by

those objects, causingthe average kineticenergy of their


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