Different substances have different thermal conductivities k, which measure how well heat is transferred by molecular collisions. The heat flow rate per unit area H is defined by: where ΔT is the difference in temperature over a distance L. The tiled part of a floor in a room feels colder than the carpeted part because:

Question

Different substances have different thermal conductivities k, which measure how well heat is transferred by molecular collisions.  The heat flow rate per unit area H is defined by:  where ΔT is the difference in temperature over a distance L.  The tiled part of a floor in a room feels colder than the carpeted part because:

Quizplus · Accepted Answer

11ecba2d_1333_81f1_a3bf_65915c489a4e_MD0008_00 Heat is transferred from one location to another by the distinct processes of conduction, convection, and radiation. In conduction, intermolecular collisions cause the movement of heat between high- and low-temperature regions because molecules within high-temperature regions tend to move faster and therefore have larger kinetic energies. High-speed molecules impart kinetic energy by colliding with nearby slower-moving molecules, transferring thermal energy. As the cascade of intermolecular collisions continues, heat is transferred over a distance (L). The rate of heat transferred (H) from a high-temperature region (T_h) to a low-temperature region (T_c) is directly proportional to the thermal conductivity (k) of the material adjoining them but inversely proportional to L: 11ecba2d_1333_81f2_a3bf_3927da462438_MD0008_00 11ecba2d_1333_81f3_a3bf_131753e31bda_MD0008_00 Thermal conductivity k measures how well a material transfers heat at a specified temperature gradient. For example, in metals, k is proportional to electrical conductivity (σ) because both conduction processes occur via the free electrons in a metal. For a person straddling the tile and carpet, the temperature gradient between the body and each object is the same because the carpet and the tile are at the same (room) temperature. However, tile is a better thermal conductor than carpet and therefore has a higher k. Consequently, heat transfer from the body to the tile is more rapid than the heat transfer to the carpet such that the person perceives the tile being colder than the carpet. (Choice A) Both the tile and the carpet are the same temperature, but the heat flow rate differs because tile has a higher k. (Choice C) If carpet had a higher thermal conductivity than tile, it would feel relatively cold to the touch. Instead, carpet feels warmer because it is more of a thermal insulator. (Choice D) Heat travels the same distance from the body into the tile and the carpet. However, the heat flow rate (and human perception of temperature) differs because tile has a higher k. Educational objective: The rate of heat transfer through conduction depends on the thermal conductivity of a substance. Objects at the same temperature but with different thermal conductivity are perceived to be different temperatures.

Different Substances Have Different Thermal Conductivities K, Which Measure How