【物理 - 筆記】Heat Transfer

1. A metal surface feel colder than a wooden surface. Why? (4M)

Metal is a poor insulator of heat. It transmits energy away from our hand more quickly by conduction and we will feel colder.

Wood is a good insulator of heat. It transmits energy away from our hand more slowly by conduction and we will feel warmer.

2. How could the fur of the polar bear and the feather of the birds keeps them warm? (3M)

Trapped air between the feathers is a poor conductor of heat and it prevents heat loss from the polar bears and the birds to the surroundings by conduction. Therefore, polar bears can keep warm in the fur while birds keep warm in their feathers.

3. Explain why air-conditioner is always installed high on the wall. (4M)

It is because it gives out cold air which falls. This pushes up the warm air, which is taken in by the air-conditioner and cooled. Convection current is set up. The room is then cooled evenly and quickly.

4. In Chinese herbal teashops, bowls of herbal tea are usually covered by glass plate. Explain how can this keep the herbal tea hot in the bowl. (2M)

Warm air from the herbal tea rise. The glass plate is to prevent energy loss from the hot herbal tea to the surroundings by convection. Therefore, the herbal tea will be cooled down more slowly.

5. Explain why fuel storage tanks are painted silvery. (3M)

The storage tank that is painted silvery is a poor absorber of heat. It prevents heat gain from surroundings to tank by radiation. Therefore, the tank will not be overheat by radiation.

6. Explain why an astronaut’s spacesuit is silvery in color. (4M)

When facing the sun, shiny surfaces are poor absorbers of heat. It prevents heat gain from the surroundings to the astronaut by radiation. Therefore, the astronaut will not be so hot.

Under very cold environment, shiny surfaces are poor radiators of heat. It prevents heat loss from the astronaut to the surroundings by radiation. Therefore, the astronaut will not be so cold. 

Important notes -_heat_transfer (pdf) from ken1470