Question

this is a lava lamp. when the light bulb heats the wax, the wax rises. when the wax cools, it falls. this cycle of rising/falling is an example of: radiation. thermal equilibrium conduction. convection.

Explanation:

• Radiation: Transfer of heat via electromagnetic waves (e.g., sunlight). Not relevant here as it's about wax movement due to heating/cooling.
• Thermal equilibrium: State where no net heat transfer occurs. The wax is in a cycle of heating and cooling (not equilibrium).
• Conduction: Heat transfer through direct contact (e.g., heat through a metal rod). Not about bulk movement of a fluid (wax here acts like a fluid when heated).
• Convection: Involves heat transfer through the bulk movement of fluids (liquids or gases). When wax is heated, it becomes less dense and rises (fluid - like movement), cools, becomes denser and falls. This cycle is convection.

Answer:

Convection.