(a)(i) Explanation of latent heat When a substance is changing state, it absorbs/gives out thermal/heat energy which does not result in temperature change. This heat absorbed or given out during change of state is known as latent heat. (ii) Factors that affect the rate of evaporation of a liquid - exposed surface area of the liquid - temperature of the liquid - wind / draught - humidity / amount of water vapour - nature of the liquid - air pressure. (b) Explanation of observations (i) Water in a clay pot is cooler than water in a closed plastic container The clay pot has pores which allow evaporation to take place. In the process of evaporation, molecules take latent heat from the bulk of the water, leaving the water cooler; but the plastic container does not have pores (to allow for evaporation). (ii) Food gets cooked faster in a pressure cooker than in an ordinary cooking pot With the pressure cooker, increased pressure raises the boiling point of water within a short period. This leads to faster cooking. Ordinary cooking pot operates at normal atmospheric pressure. (c) Effects of heat on a substance Change of/in: - state - temperature - dimension - colour - electrical resistance (d) (i) Determination of latent heat of fusion of the body Heat supplied by electric heater in the first 1400 s IVt\(_1\) = mlf mlf = 12 x 40 x 1400 = 6.72 x 105J (ii) Determination of Specific heat capacity of the body IVt\(_2\) = mc\(\Delta \theta\) c = \(\frac{IVt_2}{m \Delta \theta}\) = \(\frac{12 \times 40 \times 72}{1.5 \times 60}\) = 384 Jk\(^{-1}\) K\(^{-1}\)