Answer:
b. Fluids
Explanation:
Convection is one of the three methods of transfer of heat. Let's define them all:
- Conduction: conduction occurs when two objects (or two substances) are in contact with each other; heat is transferred from the warmer object to the colder object by the collisions between the particles of the warmer object (which have on average greater kinetic energy) and the particles of the colder object (which have on average smaller kinetic energy). This type of heat transfer can occur in solids, liquids and gases.
- Convection: convection occurs when there is a fluid which is heated from a heat source. As the part of the fluid closer to the heat source becomes warmer, it becomes less dense and it expands, rising and being replaced by the part of the fluid which is colder. Then, the mechanism continues, generating a convection current (like a cycle) which transport the heat over the whole fluid. This method of heat transfer occurs in fluids (liquids and gases) only.
- Radiation: radiation occurs when heat is carried by electromagnetic waves (which transport energy, so also heat, through space). Radiation can occur in any medium, and can also occur in vacuum since electromagnetic waves can travel in vacuum as well.
