iGCSE Physics (0625) 2.3.2 Convection-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
Heat transfer through the solid glass occurs via conduction, where thermal energy is passed through atomic vibrations. In the liquid water, the main method is convection; as water at the bottom heats up, its density decreases, causing it to rise and create a circulation current. While radiation exists, it is not the primary mechanism for these specific media. Consequently, the heat moves through the solid beaker by conduction and circulates within the fluid water by convection. This identifies Row B as the correct description of the primary thermal processes involved.
▶️ Answer/Explanation
Detailed solution:
When air is heated, the particles gain kinetic energy and move further apart, causing the air to expand. Since the same mass now occupies a larger volume $V$, the density $\rho$ decreases according to $\rho = \frac{m}{V}$. This less dense, warmer air rises while cooler, denser air sinks to take its place. This bulk movement of fluid caused by density differences is the primary mechanism of thermal energy transfer in gases known as convection. Therefore, the density decreases and the resulting transfer is convection, as shown in Row B.
▶️ Answer/Explanation
Detailed solution:
When a region of a liquid is heated, its particles move faster and spread further apart, causing the volume to increase.
Since $\text{density} = \frac{m}{V}$, an increase in volume leads to a decrease in density for that portion of the fluid.
This less dense, buoyant liquid rises upward, while cooler, denser liquid sinks to take its place, creating a circulation movement.
This specific process of heat transfer through the bulk movement of molecules in fluids is known as convection.
Options A and D refer to transfer via lattice vibrations/electrons or electromagnetic waves, which do not rely on density-driven fluid motion.