Final answer:
In constructing a thermometer, it is necessary to use a substance that expands linearly, such as in an alcohol or mercury thermometer.
Step-by-step explanation:
In constructing a thermometer, it is necessary to use a substance that expands linearly. When a substance expands linearly, its length increases proportionally with temperature. This property is crucial for accurate temperature measurement.
For example, in an alcohol or mercury thermometer, the liquid expands when heated and contracts when cooled, much more so than the glass tube that contains the liquid. The expansion of the liquid provides a large change in length for a small change in temperature, making it suitable for thermometry.
On the other hand, thermal conductivity, boiling point, and specific heat are not necessary requirements for constructing a thermometer, although they may have an impact on its performance in certain situations.