Illustration 19.1: Specific Heat

mass =  kg

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Specific heat (which is sometimes also called the specific heat capacity) describes how much heat is required to increase the temperature of a given quantity of material. In this Illustration a blue mass sits in an insulated oven (time is given in minutes and temperature is given in degrees Celsius). Restart. Assume that the block absorbs all the heat from the heater. Not surprisingly, a higher-powered heater (the amount of heat delivered/second) will result in a higher temperature of the blue mass during the same time interval. Notice that as you change the mass of the object, the temperature change is different (for a given power of the oven). The quantitative description of this is given by the equation

Q = mc (Tf - Ti)

where Q is the heat, m is the mass, c is the specific heat, and T is the temperature (with subscripts indicating final and initial temperatures). Note that if you double the mass, for the same total heat delivered, the temperature change will be cut in half. Different materials have different values of specific heat (or specific heat capacity). Water has a much higher specific heat than copper, for example. This is why it doess not take long for a copper kettle on the stove to increase in temperature in comparison with the water inside. Furthermore, with a full kettle of water, the water is more massive, so it also takes longer to reach an acceptable final temperature (usually around 100oC to boil).

Note that the specific heat usually has units of joules/(kg ⋅ Co), where Co represents a change in temperature (your text book may or may not follow this notation).

Illustration authored by Anne J. Cox.

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