Heat, Temperature, Expansion and Heat Transfer

8/12/2019 Heat, Temperature, Expansion and Heat Transfer

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2010 Pearson Education, Inc.

Conceptual Physics11th Edition

TEMPERATURE, HEAT, EXPANSION

AND HEAT TRANSFER


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This lecture will help you understand:

TemperatureHeatSpecific Heat CapacityThermal ExpansionHeat Transfer


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Temperature

A number that corresponds to the warmth orcoldness of an object

Measured by a thermometer

Is a per-particle property

No upper limit

Definite limit on lower end


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Temperature is proportional to the averagetranslational kinetic energy per particle in asubstance.

Gashow fast the gas particles are bouncing to and fro

Liquidhow fast particles slide and jiggle past one another

Solidhow fast particles move as they vibrate and jiggle in place

Temperature


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Thermometer

Measures temperature by expansion orcontraction of a liquid (mercury or coloredalcohol)

Reading occurs when the thermometer and theobject reach thermal equilibrium (having the sameaverage kinetic energy per particle)

Infrared thermometers operate by sensing IRradiation

Temperature


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Celsius Anders Celsius (17011744) 0C for freezing point of water to 100C for boiling

point of water

Fahrenheit G. D. Fahrenheit (16861736) 32F for freezing point of water to 212F for boiling

pointof water

Kelvin Lord Kelvin (18241907)

273 K for freezing point of water to 373 K for boilingpoint of water 0 at absolute zero; same size degrees as Celsius scale kelvins, rather than degrees, are used

Temperature


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There is twice as much molecular kinetic energy in 2

liters of boiling water as in 1 liter of boiling water.Which will be the same for both?

A. Temperature

B. Thermal energyC. Both A and B.

D. Neither A nor B.

Temperature

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There is twice as much molecular kinetic energy in 2

liters of boiling water as in 1 liter of boiling water.Which will be the same for both?

A. Temperature

B. Thermal energyC. Both A and B.

D. Neither A nor B.

Explanation:

Average kinetic energy of molecules is the same, whichmeans temperature is the same for both.

Temperature

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To say that body A has a higher temperature thanbody B is to say that body A has more

A. internal energy.

B. mass.C. kinetic energy per particle.

D. potential energy.

Temperature

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Internal energy transferred from one thing to

another due to a temperature difference Internal energy in transit

Flow of internal energy

From a high-temperature substance to a low-temperature substance until thermal equilibrium

is reached

Internal energy never flows unassisted from alow-temperature to a high-temperature substance

Heat



If a red-hot thumbtack is immersed in warmwater, the direction of heat flow will be fromthe

A. warm water to the red-hot thumbtack.

B. red-hot thumbtack to the warm water.

C. There will be no heat flow.

D. Not enough information.

Heat

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If a red-hot thumbtack is immersed in warmwater, the direction of heat flow will be fromthe

A. warm water to the red-hot thumbtack.

B. red-hot thumbtack to the warm water.

C. There will be no heat flow.


Heat

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Measured in joules or calories

4.18 joules of heat are required to changethe temperature of 1 gram of water by 1Celsius degree

4.18 joules = 1 calorie

Quantity of Heat


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Energy ratings of foods and fuels are determinedfrom energy released when they are burned.Unit of energy, the Calorie, is common for foods.

Heat unit for labeling foodkilocalorie or 1000 calories called acalorie

A calorie is the heat needed to change thetemperatureof 1 kg of water by 1C

Quantity of Heat

Q tit f H t


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The same quantity of heat is added to

different amounts of water in two equal-sizecontainers. The temperature of the smalleramount of water

A. decreases more.B. increases more.

C. does not change.


Quantity of Heat

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Q tit f H t


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The same quantity of heat is added to

different amounts of water in two equal-sizecontainers. The temperature of the smalleramount of water

A. decreases more.B. increases more.

C. does not change.


Quantity of Heat

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Q tit f H t


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You heat a half-cup of tea and its temperaturerises by 4C. How much will the temperaturerise if you add the same amount of heat to afull cup of tea?

A. 0CB. 2C

C. 4C

D. 8C

Quantity of Heat

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Defined as the quantity of heat required tochange the temperature of a unit mass of thesubstance by 1 degree Celsius

Like thermal inertiaresistance of a substance to

a change in temperature

Specific Heat Capacity


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Different substances have different thermalcapacities for storing energy.

Example:Takes about 2 minutes to raise the temperature

of an iron pot of water to boiling temperature

Takes less than 1 minute to raise thetemperature of the same quantity of water in asilver pot to boiling temperature



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Equal masses of different materials requireddifferent quantities of heat to change theirtemperatures by a specified number of degrees.

1 gram of water requires 1 calorie of energy toraise the temperature 1 degree Celsius.

1 gram of iron requires 1/8 as much energy for

the same temperature increase.


Therefore, water absorbs more heat than iron for the

same change in temperature. Water has a higher

specific heat.


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The high specific heat capacity of water

Allows it to store more energy without increasing itstemperature.

Allows more molecular movements without increasingits temperature.


Why is water used as coolants in mostpower plants?


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Specific heat affects climate For Europeans, the Atlantic Ocean current carries warm

water northeast from the Caribbean regions and retainsmuch of its internal energy long enough to reach theNorth Atlantic Ocean. Energy released is carried by

westerly winds over the European continent.



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Specific heat affects climate (continued) In the United States, winds in North America

are mostly westerly. On the West Coast, airmoves from the Pacific Ocean to the land. In

winter months, the ocean water is warmer thanthe air. Air blows over the warm water and thenmoves over the coastal regions. This produces awarm climate.

On the East Coast, air moves from the land tothe Atlantic Ocean. Land with lower specificheat capacity gets hot in the summer and coolin the winter.



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Which has the higher specific heat capacity, water or land?

A. Water

B. Land

C. Both of the above are the same.

D. None of the above.


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Explanation:

A substance with small temperature changes for largeheat changes has a high specific heat capacity. Water takesmuch longer to heat up in the sunshine than does land.This difference is a major influence on climate.


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Due to rise in temperature of asubstance, molecules jiggle faster

and move farther apart.

Most substances expand when heated and contractwhen cooled.

Railroad tracks laid on winter days expand and canbuckle in hot summer.

Warming metal lids on glass jars under hot waterloosens the lid by more expansion of the lid thanthe jar.

Thermal Expansion


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Plays a role in construction and devices.

Example:Use of reinforcing steel with the same rate of

expansion as concreteexpansion joints on

bridges.

Gaps on concrete roadways and sidewalks allow forconcrete expansion in the summer and contraction

in the winter.

Thermal Expansion


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Different substances expand at different rates.

Example: When the temperature of a bimetallic strip of brass and

iron is increased, greater expansion occurs for the brass

strip, which bends to turn a pointer, to regulate a valve, orto close a switch.

Bimetallic strips are used in heaters, oven thermometers,refrigerators, and electric toasters.

Thermal Expansion

Thermal Expansion


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When stringing telephone lines between polesin the summer, it is advisable to allow the linestoA. sag.

B. be taut.C. be close to the ground.

D. allow ample space for birds.

Thermal Expansion

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Thermal Expansion


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When stringing telephone lines between polesin the summer, it is advisable to allow the linestoA. sag.

B. be taut.C. be close to the ground.


Thermal Expansion

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Explanation:Telephone lines are longer in a warmer summer and shorter in acold days. Hence, they sag more on hot summer days than inwinter. If the lines are not strung with enough sag in summer,they might contract too much and snap during the winterespecially when carrying ice.

Thermal Expansion


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When stringing telephone lines between poles in the summer,

it is advisable to allow the lines toA. sag.

B. be taut.

C. be close to the ground.


Explanation:

Telephone lines are longer in a warmer summer and shorter in a coldwinter. Hence, they sag more on hot summer days than in winter. Ifthe lines are not strung with enough sag in summer, they mightcontract too much and snap during the winterespecially whencarrying ice.

Thermal Expansion

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Increases in expansion are greater in liquids than in

solids.

Example:

Overflow of gasoline from a cars tank on ahot day

Reason:Gasoline underground is cool, but whenplaced in the cars tank, it warms andexpands.

Thermal Expansion


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Expansion of water

When water becomes ice, it expands. Ice has open-structured crystals resulting from strong bonds atcertain angles that increase its volume. This makeice less dense than water.

Thermal Expansion


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Thermal Expansion

Thermal Expansion


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When a sample of 0C water is heated, it first

A. expands.

B. contracts.

C. remains unchanged.


Thermal Expansion

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Thermal Expansion


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When a sample of 0C water is heated, it first

A. expands.

B. contracts.



Thermal Expansion

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Explanation:Water continues to contract until it reaches atemperature of 4C. With further increase in

temperature beyond 4C, water then expands.

Thermal Expansion


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When a sample of 4C water is cooled, it

A. expands.

B. contracts.



Thermal Expansion

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Thermal Expansion


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When a sample of 4C water is cooled, it

A. expands.

B. contracts.



e a pa s o

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Explanation:Parts of the water will crystallize and occupy morespace.


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Objects in thermal contact at differenttemperatures tend to reach a commontemperature in three ways:

ConductionConvectionRadiation

Heat Transfer and Change of Phase


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Transfer of internal energy by electronand molecular collisions within asubstance, especially a solid

Conduction

The electrons carryinghigh energy travel from

end to end of thematerials just likedistributing the energy.


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Good conductors conduct heatquickly.

Substances with loosely held electronstransfer energy quickly to other electronsthroughout the solid.Example: Silver, copper, and other solid metals

Conduction


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Poor conductors are insulators.molecules with tightly held electrons in asubstance vibrate in place and transferenergy slowlythese are good insulators

(and poor conductors).Example: Glass, wool, wood, paper, cork, plasticfoam, air

Substances that trap air are goodinsulators.Example: Wool, fur, feathers, and snow

Conduction

Conduction


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If you hold one end of a metal bar against a

piece of ice, the end in your hand will soonbecome cold. Does cold flow from the ice toyour hand?

A. YesB. In some cases, yes

C. No

D. In some cases, noExplanation:

Cold does not flow from the ice to your hand. Heat flowsfrom your hand to the ice. The metal is cold to your touchbecause you are transferring heat to the metal.

CHECK YOUR NEIGHBOR


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InsulationDoesnt prevent the flow of internal energy

Slows the rate at which internal energy flows

Example:Rock wool or fiberglass between walls slows thetransfer of internal energy from a warm house to acool exterior in winter, and the reverse in summer.

Conduction


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Dramatic example:

Walking barefoot without burning feet onred-hot coals is due to poor conductionbetween coals and feet.

Conduction

This is done quickly!


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Transfer of heat involving only

bulk motion of fluids

Example: Visible shimmer of air above a hot

stove or above asphalt on a hotday Visible shimmers in water due to

temperature difference

Convection


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Reason warm air risesWarm air expands, becomes lessdense, and is buoyed upward.

It rises until its density equals that ofthe surrounding air.

Example: Smoke from a fire rises and blends

with the surrounding cool air.

Convection


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Opposite to the warmingthat occurs when air iscompressed

Example: The cloudy region abovehot steam issuing from the nozzle of apressure cooker is cool to the touch (acombination of air expansion andmixing with cooler surrounding air).Careful, the part at the nozzle that youcant see is steamouch!

Convection

Convection


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Although warm air rises, why are

mountaintops cold and snow covered, whilethe valleys below are relatively warm andgreen?

A. Warm air cools when rising.

B. There is a thick insulating blanket of air abovevalleys.

C. Both A and B.

D. None of the above.Explanation:

Earths atmosphere acts as a blanket, which keepsthe valleys from freezing at nighttime.

CHECK YOUR ANSWER


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Winds

Result of uneven heating of the airnear the ground Absorption of Suns energy occurs

more readily on different parts of

Earths surface.Sea breeze

The ground warms more than waterin the daytime.

Warm air close to the ground risesand is replaced by cooler air fromabove the water.

Convection


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Transfer of energy from the Sun through emptyspace

Radiation

Radiation


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The surface of Earth loses energy toouter space due mostly to

A. conduction.

B. convection.C. radiation.

D. radioactivity.

Explanation:

Radiation is the only choice, given the vacuum ofouter space.

CHECK YOUR ANSWER

Radiation


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Which body glows with electromagneticwaves?A. Sun

B. Earth

C. Both A and B.

D. None of the above.

Explanation:

Earth glows in long-wavelength radiation,while the Sun glows in shorter waves.

CHECK YOUR ANSWER


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Transferred energyExists as electromagnetic wavesranging from long (radio waves) to

short wavelengths (X-rays)In visible region, ranges from longwaves (red) to short waves (violet)

Radiation

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Heat, Temperature, Expansion and Heat Transfer