The distance between two electricity transmission pylons is 100 m. A utility company hangs a power cable of length 104 m between them so that it hangs with some slack.
Why does the engineer use a cable that is longer than the straight-line distance between the pylons?
to allow for the thermal contraction of the cable in cold weather
to reduce the electrical resistance of the cable
to ensure the cable remains taut during hot summer days
to decrease the magnetic field strength beneath the power lines
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.