chapter 4 heat 4.2
TRANSCRIPT
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Heat content in an object depends on its type of material,
mass and temperature.
The heat capacity of an object is the quantity of heat energyrequired to increase its temperature by 1. Each object has
its own heat capacity.
The unit of heat capacity is J1 .
(when we are discussing the heat capacity, we DO NOT consider
about the mass factor!)
However , an object with a larger mass will have a large heat
capacity than an object with smaller mass of the same
material.
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Solehin places 2 pebbles of different masses and a glass ofwater under the hot afternoon Sun.
After 5 minutes, he finds that: The small pebble is hotter than the large pebble
The large pebble is hotter than water of the same mass.
sun
Water (samemass as thelarge pebble)Small
pebbleLargepebble
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The increase in temperature depends on:
The quantity of heat absorbed.
The mass of the object.
The material of an object.
Another example on the next page..
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5 J
5 J
1
If want to rise up 1must to absorb 5J ofheat capacity!
If want to rise down1 must to release5J of heat capacity!
10 J
10 J
1
If want to rise up 1must to absorb 10J ofheat capacity.
If want to rise down1 must to release10J of heat capacity.
Now, we can compare which one can easily to riseup the temperature and which one cant!!!!
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c = Q
m
Q = mc
Therefore the quantity of heat absorbedor lost by an object, Q = mc.
Specific heat capacity(J kg1 1)
Heat (J)
Temperaturechanges (/K)
(absorb / release)
Mass(Kg)
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5 J kg1 1
= 5J1kg X 1
If 1 kg of substance want to riseup 1 need to absorb 5J of heat.
If 1 kg of substance want risedown 1 need to release 5J ofheat.
10 J kg1 1
= 10J1kg X 1
If 1 kg of substance want to riseup 1 need to absorb 10J of heat.
If 1 kg of substance want to risedown 1 need to release 10J ofheat.
Caution: When we talk the temperature the mass must be constant.!!!!
Now, we can compare which one can easily to rise up thetemperature and which one cant!!!!
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900 J of heat needs to be supplied to 1kgaluminium to produce a 1C temperatureincrement.
1800J of heat needs to supplied to 2kgaluminium to produce a 1C temperatureincrement.
1800J of heat needs to supplied to 1kg
aluminium to produce a 2Ctemperatureincrement.
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Substance[solid]
Specific heatcapacity,c/ J kg1
C1
ICE (-15C) 2000
Wood 1400
Ceramic 1090Aluminium 900
Stone 840
Glass 753
Silicon 700
Steel 502Iron 452
Copper 387
Silver 235
Lead 130
Gold 129
Substance[liquid]
Specific heatcapacity,c/ J kg1
C1
Water(15) 4200
Ethanol 2450
Glycerine 2410
Parrafin 2100
Oil 1890
Benzene 1740
Mercury 140
Steam 2010
Human body 3500
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Heat Capacity Specific heatcapacity
Symbol C c
General unit Relates to a particular object:J C1
Relates to a material:J kg1C1
Value Not fixed, depends onthe mass of the object
Fixed for a materialregardless of its mass
Formula Q = C Q = mc
Relationship betweenc and C C = mc
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