iGCSE Physics (0625) 2.3.2 Convection -Exam Style Questions Paper 2 - New Syllabus
▶️ Answer/Explanation
Detailed solution:
Air heated by the radiator expands and becomes less dense than the cooler surrounding air.
This less dense, warm air rises towards the ceiling, creating the circulation pattern shown in diagram X.
As the air cools, it becomes denser and sinks, completing the convection current that heats the room.
Diagram Y is incorrect because it shows warm air sinking, which does not occur.
Thus, the correct combination is diagram X with the explanation of density change, matching Option A.
▶️ Answer/Explanation
Detailed solution:
The table shows that as height increases from $0~m$ to $40~m$, the temperature rises from $10^{\circ}C$ to $16^{\circ}C$.
This phenomenon occurs due to convection, where warmer air expands, causing its volume to increase.
Since $\rho = \frac{m}{V}$, an increase in volume results in a decrease in density $\rho$ for a fixed mass of air.
Because warm air is less dense than cool air, it experiences an upward buoyant force and rises.
This explains why the highest temperatures are recorded at the greatest heights in the cave.
Options A and B are scientifically incorrect, while D contradicts the physical behavior of fluids.
▶️ Answer/Explanation
Detailed solution:
Convection is a method of thermal energy transfer that occurs in fluids (liquids and gases).
When a liquid is heated, its particles gain kinetic energy, move further apart, and the volume increases.
According to $\rho = \frac{m}{V}$, the density decreases, causing the warmer, less dense liquid to rise.
Conversely, cooler liquid is denser and sinks to take the place of the rising warm liquid, creating a convection current.
Statement C is incorrect because it is the warmer, less dense liquid that rises, not the cooler liquid.
This process ensures that heat is distributed throughout a substance, such as water in a pan.