Chapter 5, Problem 41R

To determine

To predict: Thermal energy transfers by conduction or convection if water is heated from the top.

Explanation of Solution

Introduction:

The thermal energy of a body is the sum of kinetic energy and potential energy of all the particles that make up that body. It is dependent on various factors.

Thermal energy can be transferred in two different ways if the body is in actual contact with the heat source. It can either take place by conduction where heat is transferred due to the collision of molecules or by convection, heat can be transferred where the motion of particles in bulk take place based on their densities. Here if water is heated from the top, convection cannot be set up as in convection, when a fluid is heated, its density decreases due to which it rises upwards. In this case since water is heated from upwards, it is already at the top due to being lighter and evaporates from there only. So some heat can be transferred by conduction here if water is heated from the top as the molecules at the top may collide with the molecules nearby to transfer their thermal energy to them.

Conclusion:

Hence, if water is heated from top, thermal energy transfer can take place by conduction not by convection.