Question

which of the following are examples of convection?

hot magma rises from asthenosphere to the surface of earth as cooler more dense magma sinks back down. cycle repeats.

colder and denser seawater sinks to the bottom as warmer seawater with a lower density rises. cycle repeats.

a metallic spoon heats up near a fire.

photons traveling through a vacuum.

hot air in the atmosphere rises, cools and sinks back down to the surface of earth, where it eventually heats up again and rises. cycle repeats.

Explanation:

Convection is heat transfer via fluid (liquid/gas) movement due to density differences from heating/cooling. The first, second, and fifth options involve cyclic fluid motion (magma, seawater, air) driven by density changes from temperature differences, fitting convection. The third is conduction (heat through solid spoon), the fourth is radiation (photons in vacuum).

Answer:

Hot magma rises from asthenosphere to the surface of Earth as cooler more dense magma sinks back down. Cycle repeats., Colder and denser seawater sinks to the bottom as warmer seawater with a lower density rises. Cycle repeats., Hot air in the atmosphere rises, cools and sinks back down to the surface of Earth, where it eventually heats up again and rises. Cycle repeats.