🔍 Key Concepts

• Natural convection depends on fluid motion caused by buoyancy (density differences due to temperature differences). • As a fluid is heated, its density changes; this density difference drives the motion that carries heat. • Think about how a larger temperature difference (ΔT) affects the density difference and thus the convection strength.

💭 Think About

• If the temperature difference between hot and cold regions increases, what happens to the density difference between those regions? Larger, smaller, or unchanged? • In natural convection, does stronger buoyant force (from bigger density differences) tend to increase or decrease the heat transfer rate? • Look at each option’s wording: is heat transfer rate moving in the same direction or the opposite direction as density difference, and is density difference moving in the same or opposite direction as temperature gradient?

✅ Before You Answer

• Be clear whether a quantity is directly proportional (goes up when the other goes up) or inversely proportional (goes up when the other goes down). • Mentally test an extreme case: if the temperature gradient is very large, should the density difference and heat transfer rate be large or small in natural convection? • Eliminate any option where the described relationships don’t match how buoyancy-driven flow behaves when fluid is strongly heated from below and cooled above.