Why are overhead power lines hung with a noticeable sag (slack) between support poles?
to allow for contraction of the power lines on a cold day
to allow for expansion of the power lines on a cold day
to allow for contraction of the power lines on a hot day
to allow for expansion of the power lines on a hot day
528 exam-style questions on CIE IGCSE Physics 2.2 Thermal properties and temperature, covering 2.2.1 Thermal expansion of solids, liquids and gases, 2.2.2a Internal energy and temperature, 2.2.2b Specific heat capacity, 2.2.3a Melting, boiling, condensation and solidification, 2.2.3b Evaporation, and 2.2.3c Cooling by evaporation. Each one has a worked solution and a mark scheme showing where the marks go.