Self-assessment questions

Conduction

1. Is the heat transferred from a campfire to a person standing in front of it a good example of heat transfer by conduction?

No, because air is generally a poor conductor of heat.

2. Why is it more effective to wear a few layers of thin clothing compared to a single thick layer of clothing on a cold day?

Wearing a few layers of the thin clothing actually traps more air. Because air is a poor conductor of heat and so wearing a few layers of thin clothing is more effective than a single thick layer of clothing.


Convection

1. Is the heat transferred from a hot iron to the person holding it in a downward position for ironing a good example of heat transfer by convection?

Yes. The iron heats up the air around it. And hot air would rise and a convection current can be set up, because it is less dense. However, much of the heat transfer from a hot iron to the person doing it is by radiation.

Radiation

1. Is the heat transferred from a hot zinc roof to a person below it a good example of heat transfer by radiation? Explain.

Yes. The heat transfer could not be due to conduction or convection. Because the cold air below the zinc roof is a poor conductor of heat. Thus the convection currents of air cannot be set up from the roof to the person standing below.

2. What is the purpose of the vacuum flask that is used to store cold liquids?

It is to prevent heat gain by conduction and convection.