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| Specific Heat |
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| From the experiments, we know that the quantity of heat supplied Q is proportional to |
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 mass of the substance (m) |
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increase in temperature  t (t2 - t1) |
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| Q = S m (t2-t1)------- (1) |
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| S is the constant of proportionality. It is a characteristic feature of the substance and is known as its specific heat. From equation (1) we can write |
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| Thus, specific heat of a substance may be
defined as 'the quantity of heat required to increase the temperature of
unit mass of the substance through 1oC'. |
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| In SI system unit mass = 1 kg |
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| Specific heat is expressed in Joules/kg/K |
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| From equation 1 we have |
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| Q = m s (t2-t1) |
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| If (t2-t1) = 10C then Q is its thermal capacity. |
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| Thus, thermal capacity (Q=ms)=mass x specific heat of the substance. |
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| Thermal capacity is expressed in Joules/Kelvin. |
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| Specific heat of some of the substances |
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| Specific heat of copper is 386 J/kg/K means '1kg of copper requires 387 J of heat energy to
increase its temperature by 1k'. |
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| We may note that the specific heat of water is the highest. It requires nearly 4200 Joules of heat energy to
increase the temperature of 1 Kg of water by 1K. Infact, water has one of the highest specific heats of all matter. Liquid ammonia with a specific heat of 5040 J/Kg/Kelvin is one of the few substances with a value higher than that of water. |
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| The specific heat of a substance is an important physical property because it tells us the suitability of a given substance for a specific purpose. Aluminium vessels are used in cooking because aluminium
is a light metal. Hence, for a given volume, its thermal capacity will be
less than that of vessels made of steel of same volume. |
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| The high specific heat of water explains
why land close to a large pond of water is likely to have a milder climate
than land without a pond close by. Because of high specific heat, water on
the land gets heated slowly. Land near the pond also gets heated slowly. For
the same amount of heat, dry land gets heated quickly to a much higher
temperature. Soil is a poor conductor, prevents the heat from going deep
into the ground. Hence, the heat causes a quick rise in temperature on dry
land. For same reasons, land areas far from water-cool off much faster than
land near large bodies of water. |
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| While solids and liquids have only one specific heat, gases possess two types of specific heat |
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 specific heat at constant volume |
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 specific heat at constant pressure. |
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| When a gas absorbs heat at constant volume, all the heat energy supplied is used to rise its temperature. |
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| When a gas absorbs heat at constant pressure, part of the energy supplied is used to do external work. |
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| Therefore, specific heat at constant pressure of a gas is greater than specific heat at constant volume by an amount equal to the external work done during expansion. |
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