Spec 4.9 names three investigations — examiners may ask about any of them.
(1) Conduction. Take rods of similar shape made of different materials (copper, brass, iron, glass). Coat the ends with WAX (or attach drawing pins with wax). Heat one end of each rod uniformly. Time how long the wax melts on the far end of each rod. Best conductor → wax melts fastest.
(2) Convection. Half-fill a beaker with cold water. Drop a single crystal of potassium permanganate (purple dye) at one edge. Heat the water gently directly below the crystal. Observe the purple streak rise vertically, then loop across the top and descend on the other side → tracks the convection current.
(3) Radiation. Two identical metal cans, one painted matt black, one polished. Fill each with boiling water. Place a thermometer in each. Record temperature every 30 s for 10 min. Plot T vs t. The black can's curve falls steeper → emits IR faster.
Reducing random error. Repeat each experiment 3 times and take the mean. Control variables: same volume / same starting temperature / same room temperature / same air-flow / identical apparatus apart from the variable being tested.