A student is cooking porridge in a thin-walled aluminium pan placed over a gas flame.
(i) Identify the principal mode of heat transfer from the flame to the bottom surface of the pan and justify your answer.
(ii) Identify the dominant mode by which heat reaches the porridge from the metal base of the pan. Explain why this mode prevails inside the porridge.
(iii) State the main mode by which heat leaves the upper surface of the hot porridge to the kitchen air. Give two reasons in support of your choice.
(iv) The student now places a tight lid on the pan. Explain qualitatively how the lid alters the dominant heat transfer mechanism at the porridge surface and comment on the expected change in the time required to cook the porridge.