GED Science TestPhysical ScienceMedium
A student is heating a beaker of water on a hot plate. They notice that the water at the bottom of the beaker gets warm first, then rises, and cooler water from the top sinks to take its place, creating a circulating current. What mode of heat transfer is primarily responsible for this observation?
- AConvection
- BConduction
- CEvaporation
- DRadiation
Show answer & explanationAnswer & explanation
Correct answer: A. Convection
The movement of heated fluid itself (warm water rising, cool water sinking) is the definition of convection, a common mode of heat transfer in liquids and gases.
Why the other options are wrong
- B. Conduction is heat transfer through direct contact without mass movement.
- C. Evaporation is a phase change from liquid to gas, which can cause cooling but isn't the primary heat transfer mechanism described.
- D. Radiation is heat transfer through electromagnetic waves, without a medium.
Convection
Heat transfer that occurs through the movement of fluids (liquids or gases). Warmer, less dense fluid rises, and cooler, denser fluid sinks, creating a circulation current.
- Occurs in liquids and gases.
- Involves the physical movement of the heated substance.
- Creates convection currents.
- Examples: boiling water, ocean currents, atmospheric circulation.
Memory trick: Heat moves in three ways: contact, current, or waves.