Which of the following is NOT a method of heat transfer?

The correct choice identifies expansion as not being a method of heat transfer. Heat transfer occurs through three primary mechanisms: conduction, convection, and radiation.

Conduction involves the transfer of heat through direct contact between materials, where energy moves from the hotter to the cooler part of the object or between objects in contact. Convection refers to the transfer of heat in fluids (liquids and gases) where warmer areas of a liquid or gas rise and cooler areas sink, creating a circulation pattern that transfers heat. Radiation, on the other hand, is the transfer of heat through electromagnetic waves and does not require a medium, allowing heat to travel through the vacuum of space.

Expansion, however, relates to the physical change in volume of a substance when it is heated, which may affect how heat is distributed but is not a method of transferring heat itself. It describes a physical phenomenon rather than a mechanism of heat transfer, which is why it is the correct answer in this context.