We use the symbol Q for quantity of heat. When it is associated with an infinitesimal temperature change dl’, we call it dQ. The quantity of heat Q required to increase the temperature of a mass m of a certain material from T, to T2 is found to be approximately proportional to the temperature change l:!.T= T2 – T1• It is also proportional to the mass m of material. When you’re heating water to make tea, you need twice as much heat for two cups as for one if the temperature interval is the same.

The quantity of heat needed also depends on the nature of the material; raising the temperature of one kilogram of water by I Co requires 4190 J of heat, but only 910 J are needed to raise the temperature The specific heat capacity of a material always depends somewhat on the initial temperature and the temperature interval.

Figure 15-10 shows this variation for water. In the problems and examples in this chapter we will usually ignore this small variation.of one kilogram of aluminum by 1Co


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