A metal ring is heated in an oven. What happens to the diameter of the hole in the center of the ring?
AIt decreases — the expanding metal fills available space inward
BIt stays the same — the hole is empty space and heat doesn't affect it
CIt increases — the entire ring, including the hole, expands uniformly
DIt depends on the thickness of the ring walls
The entire object scales up uniformly when heated, including any holes or voids. The atoms bounding the hole move away from each other just as all other atoms do — think of it like enlarging a photocopy where every feature, including holes, grows proportionally. Options A and B represent the common misconception that material 'flows in' to fill the hole. In reality, a metal ring's bore expands when heated, which is why a stuck metal lid loosens under hot water.
Question 2 Multiple Choice
At which temperature does liquid water reach its maximum density?
A0°C — just before freezing
B4°C — where hydrogen bonding produces the most compact liquid structure
C100°C — just before boiling, when kinetic energy is highest
D−10°C — deep in the solid ice phase
Water behaves anomalously near freezing. Cooling from room temperature, it contracts normally until 4°C. Below 4°C, hydrogen bonds begin reorganizing toward the open tetrahedral ice structure, and water starts to expand as it cools further. At 0°C, ice is about 9% less dense than liquid water. Maximum density is at 4°C. This is why lakes freeze from the surface down, not from the bottom up.
Question 3 True / False
A liquid-in-glass thermometer works partly because of thermal expansion — the liquid rises when heated and falls when cooled.
TTrue
FFalse
Answer: True
Liquid-in-glass thermometers rely directly on thermal expansion. The liquid (historically mercury, now often alcohol) expands predictably with temperature increases, rising up a narrow calibrated tube. The narrow bore amplifies small volume changes into easily readable length changes. The same principle — differential thermal expansion between two materials — drives bimetallic strip thermostats.
Question 4 True / False
Water is denser as solid ice than as liquid water, which is why ice sinks.
TTrue
FFalse
Answer: False
Ice is less dense than liquid water — this is water's key anomaly. When water freezes, hydrogen bonds form an open tetrahedral lattice with more empty space than liquid water, increasing volume by about 9%. Because density = mass/volume, larger volume at the same mass means lower density. Ice therefore floats. For nearly every other substance, the solid phase is denser than the liquid.
Question 5 Short Answer
Explain why a metal lid that is stuck on a glass jar can often be loosened by running it under hot water.
Think about your answer, then reveal below.
Model answer: Metal typically has a larger coefficient of linear thermal expansion (α) than glass. Hot water heats the lid, causing the metal to expand more than the glass jar. The lid's opening grows by a larger amount than the jar's rim, loosening the fit and breaking the seal.
This is a practical application of differential thermal expansion. The key is that different materials have different α values, so they expand by different amounts for the same temperature increase. Engineers exploit this property intentionally — and must guard against it causing unwanted stress in structures like bridges and pipelines.