iGCSE Physics (0625) 2.2.1 Thermal expansion of solids, liquids and gases-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
When the temperature increases on warm days, the metal railway tracks undergo thermal expansion.
This occurs because the particles in the solid vibrate more vigorously, increasing their average separation.
The expansion causes the length of each track section to increase by a value $\Delta l$.
Without the gaps, the expanding rails would press against each other, leading to dangerous buckling or deformation.
The gaps provide the necessary space for this increase in volume and length to occur safely.
Therefore, the gaps are specifically required because the tracks expand on warm days.
▶️ Answer/Explanation
Detailed solution:
When the balloon is held above the heater, thermal energy is transferred to the air particles inside.
According to the kinetic particle model, as the temperature $T$ increases, the average kinetic energy of the particles also increases.
These faster-moving particles collide with the inner walls of the balloon more frequently and with greater force.
To maintain a pressure balance with the outside atmosphere, the internal volume $V$ must increase.
This process is known as thermal expansion, specifically where the air (gas) inside the balloon expands.
While the rubber material may stretch, the primary “cause” of the significant volume increase is the expansion of the air itself.
▶️ Answer/Explanation
Detailed solution:
When temperature increases, solids undergo thermal expansion, causing dimensions like length and diameter to increase. Since volume $V$ increases while mass $m$ remains constant, the density $\rho = \frac{m}{V}$ must decrease. Mass is a measure of the quantity of matter in an object and is independent of temperature or volume changes. Therefore, while the density (A), diameter (B), and length (C) all change due to expansion, the mass of the metal coin (D) remains constant.