(a)
For the correct answer:
(heated air) expands
(becomes) less dense
less dense air rises OR denser air sinks
Air heated by the wood burner expands and becomes less dense than the surrounding cooler air. This less dense, warmer air rises, while denser, cooler air sinks to replace it near the burner. This continuous circulation of air, known as a convection current, transfers thermal energy throughout the cabin, warming the space.
(b)(i)
For the correct answer:
(dull black is) best / better / good emitter owtte of radiation / infrared
Dull, black surfaces are excellent emitters of thermal radiation (infrared). The chimney efficiently radiates heat energy from the hot gases inside it out into the room, warming the cabin air and surfaces directly.
(b)(ii)
For the correct answer:
(shiny foil is) best / better / good reflector of radiation / infrared
Shiny, light-coloured surfaces are poor emitters but very good reflectors of thermal radiation. The foil reflects infrared radiation emitted from the wood burner and chimney back into the cabin, preventing it from being absorbed and lost through the wall.
