Why α : β : γ is 1 : 2 : 3, how a hole and a bimetallic strip behave, why a pendulum clock loses time in summer, and the real-against-apparent expansion of a liquid in its vessel.
Unit 2 carries 7 of the 50 physics marks; with six chapters sharing them, this one averages a little over one (MEC publishes weights by unit, not by chapter). Almost everything here is one formula, ΔL = L₀αΔθ, repeated in one, two and three dimensions, so it is the fastest chapter in the unit to finish and among the most reliable to score.
The MEC scope lines are: Linear, superficial and cubical expansion; Real and apparent expansion of liquids. The headings below are those two points, in MEC's order.
Three ways it is asked: recall (the ratio α : β : γ, the temperature of maximum density of water, which metal goes on the outside of a bimetallic strip on heating); understanding (whether a hole gets bigger or smaller, why a pendulum clock loses time in summer, why the level in a flask first falls and then rises when the flask is plunged into hot water); application (an expansion in millimetres, the overflow from a full vessel, a real coefficient from an apparent one, the seconds a clock loses in a day).
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