What type of heat transfer occurs when a fluid is heated, causing it to expand and become less dense?

The correct choice pertains to convection, which is the type of heat transfer that occurs in fluids (liquids and gases) when they are heated. In this process, as the fluid is heated, it expands, decreases in density, and rises due to buoyancy. This rising motion of less dense fluid creates a current, allowing heat to be distributed throughout the fluid as it interacts with cooler areas.

Convection is essential in various applications, such as in heating systems or natural processes like atmospheric circulation. When considering the other forms of heat transfer: conduction involves direct transfer of heat between materials in contact, radiation transfers heat through electromagnetic waves, and thermography is a technique used to visualize heat distribution rather than being a method of heat transfer itself. Understanding why convection is the correct choice helps clarify the distinctions among these concepts and their applications in different scenarios.