vii-science heat -ppt.pdf

ABCD

1. CLASS-VII
SCIENCE
CHAPTER 4 -HEAT
Prepared by:
P M THANKACHAN
AECS-2, KALPAKKAM
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2. HOT OR COLD
Inourday-to-daylife,wecomeacrossanumberofobjects.
•Someofthemarehotandsomeofthemarecold
•Teaishotandiceiscold.
•Usuallyweidentifythembytouching.Butwecannotalways
relyonoursenseoftouchtodecidewhetheranobjectishotor
cold.Sometimesitmaydeceiveus.
•Thenhowdowefindouthowhotanobjectreallyis?
•Areliablemeasureofthehotnessofanobjectisits
temperature.
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3. MEASURING TEMPERATURE
Temperatureismeasuredbyadevicecalledthermometer.
Therearedifferenttypesofthermometers.
1.Clinicalthermometer
2.Laboratorythermometer
3.Maximum-minimumthermometer
4.Digitalthermometer.
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4. 1. CLINICAL THERMOMETER
•Thethermometerthatmeasuresourbodytemperatureis
calledaclinicalthermometer.
•Aclinicalthermometerconsistsofalong,narrow,uniform
glasstube.Ithasabulbinoneendwhichcontainsmercury.
Outsidethebulb,ashiningthreadofmercurycanbeseen.
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5. •Wecanalsoseeascaleonthethermometer.Thescalewe
useisCelsiusscaleindicatedby⁰C.
•Kinkpreventsmercurylevelfromfallingonitsown
•Theclinicalthermometerisdesignedtomeasurethe
temperatureofthehumanbodyonly..
•Thetemperatureofthehumanbodydoesnotgobelow
35⁰Corabove42⁰C.
•Thatisthereasonthatthisthermometerhastherange
from35⁰Cto42⁰C.
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6. HOW TO USE A CLINICAL
THERMOMETER?
•Washthethermometer,preferablywithanantiseptic
solution.
•Holditfirmlyandgiveitwithafewjerks.Thejerkwill
bringthelevelofmercurydown.Ensurethatitfallsbelow
35⁰C.
•Nowplacethebulbofthethermometerunderyourtongue.
•Afteroneminute,takethethermometeroutandnotethe
reading.Thisisyourbodytemperature.
•Thetemperatureshouldalwaysbestatedwithitsunit.
•Thenormaltemperatureofthehumanbodyis37⁰C.
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7. PRECAUTIONS TO BE OBSERVED
WHILE READING A CLINICAL
THERMOMETER
•Thermometershouldbewashedbeforeandafteruse,
preferablywithanantisepticsolution.
•Ensurethatbeforeusethemercurylevelisbelow35⁰C.
•Readthethermometerkeepingthelevelofmercuryalong
thelineofsight.
•Handlethethermometerwithcare.Ifithitsagainstsome
hardobjects,itcanbreak.
•Don’tholdthethermometerbythebulbwhilereadingit.
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8. 2. LABORATORY
THERMOMETER
•The range of laboratory thermometer
is -10⁰C to 110⁰C .
•It is used in laboratories to measure
temperature with high accuracy.
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9. PRECAUTIONS TO BE OBSERVED
WHILE READING A LABORATORY
THERMOMETER
•In addition to the precautions needed while reading a
clinical thermometer, the laboratory thermometer
•Should be kept upright, not tilted.
•The bulb should be surrounded from all sides by the
substance of which the temperature should be measured.
•The bulb should not touch the surface of the container.
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10. 3.MAXIMUM –
MINIMUM
THERMOMETER
•Themaximumandminimum
temperaturesoftheprevious
day,reportedinweather
reports,aremeasuredbythis
thermometer.
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11. 4.DIGITAL THERMOMETER
•Thereisalotofconcernovertheuseof
mercuryinthermometers.
•Mercuryisatoxicsubstanceandisvery
difficulttodisposeof,ifathermometer
breaks.
•Digitalthermometersdonotuse
mercury.
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12. TRANSFER OF HEAT
Transferofheattakesplacethrough
•conduction
•convection
•radiation
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13. CONDUCTION
The process by which heat is
transferred from the hotter end
to the colder end of an object is
known as conduction. In solids,
generally, the heat is transferred
by the process of conduction.
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14. CONDUCTORS AND INSULATORS
•Conductors-Thematerialswhichallowheattopass
throughthemeasilyareconductorsofheat.
Eg:-Aluminium,iron,copper
•Insulators-Thematerialswhichdonotallowheattopass
throughthemeasilyarepoorconductorsorinsulatorsof
heat.
Eg:-Plastic,wood,rubber
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15. CONVECTION
Thetransferofheatbythe
movementofafluid(liquid
orgas)betweentheareasof
differenttemperature.
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16. SEA
BREEZE
AND
LAND
BREEZE
Seabreeze
Duringtheday,thelandgets
heatedfasterthanwater.Theair
overthelandbecomeshotterand
risesup.Thecoolerairfromthe
searushesintowardsthelandto
takeitsplace.Thewarmairfrom
thelandmovestowardstheseato
completethecycle.Theairfrom
theseaiscalledtheseabreeze.
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17. SEA
BREEZE
AND
LAND
BREEZE
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18. SEA
BREEZE
AND
LAND
BREEZE
Land Breeze
Atnight,itisexactlythereverse.
Thewatercoolsdownmoreslowly
thantheland.Sothecoolairfrom
thelandmovestowardsthesea.
Thisiscalledthelandbreeze.
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19. RADIATION
•Itisthetransferof
heatwhichdoesnot
requireanymedium.
•Eg:-Fromthesun
heatcomestousby
radiation.
•Ahotutensilkept
awayfromtheflame
coolsdown.
•Wegetheatfromthe
roomheater.
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20. KINDS OF CLOTH WE WEAR IN
SUMMER AND WINTER
•Insummerwepreferlightcolouredclothesandinwinter
usuallyweardarkcolouredclothes.
•Lightcolouredclothesreflectsmostoftheheatfallson
them,andtherefore,wefeelmorecomfortablewearing
theminthesummer.
•Darksurfacesabsorbmoreheatandwefeelmore
comfortablewithdarkcolouredclothesinthewinter.
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21. WOOLLEN
CLOTHES KEEP US
WARM IN WINTER
•Wool is a poor conductor of
heat.
•Air is trapped in between
the wool fibers. This air
prevents the flow of heat
from our body to the cold
surroundings. So, we feel
warm.
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22. THANK YOU
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