Transfer of Thermal Energy

Choose the most appropriate statement that describes thermal energy transfer.

• Heat flows from a hotter body to a colder body, and coldness flows in the opposite direction.

• Conduction is one process of thermal energy transfer that involves the vibration of particles.

• There is no heat flow when two bodies are in thermal equilibrium.

• Radiation refers to the process of heat transfer by the movement of fluid due to density differences.

1. Two similarly sized blocks (one made out of metal, and the other, wood) are in contact with each other. The metal block is at a higher temperature than the wooden block. Describe what is likely to happen to both blocks.

• The metal block transfers some of its temperature to the wooden block, causing the wooden block to gain temperature.

• The metal block gets hotter and the wooden block gets cooler due to net thermal energy transfer from the wooden block to the metal block.

• The metal block and the wooden block eventually reach thermal equilibrium with each other, and there will be no net thermal energy transfer between them.

• The metal block and the wooden block cannot reach thermal equilibrium even after a long time since they are made of different substances.

In the early morning, Ali touches the surface of a car body and finds that it is cold. This is because the metallic surface of the car is a good

• thermal conductor and it conducts heat from the surface to Ali’s hands.

• thermal conductor and it conducts heat from Ali’s hands to the surface.

• thermal insulator and it does not conduct heat from the surface to Ali’s hands easily.

• thermal insulator and it does not conduct heat from Ali’s hands to the surface easily.

Which of the following shows the correct order of the three states of matter arranged in the order of best thermal conductivity to worst thermal conductivity?

• Solid, gas, liquid

• Gas, liquid, solid

• Liquid, gas, solid

• Solid, liquid, gas

A metal gauze is wrapped around a piece of ice and dropped into a boiling tube containing water. The top of the boiling tube is then heated up by a Bunsen burner until the water near the surface begins to boil, as shown in the diagram below. During this time, the ice is observed to remain largely un-melted. This experiment shows that

• ice is a poor conductor of heat.

• water is a good conductor of heat.

• water is a poor conductor of heat.

• metal gauze is a good conductor of heat.

A lamp has been switched on for a while. Siti, who is sitting beside it, begins to feel its heat. This heat transfer is largely due to

• conduction from the lamp through the air to Siti.

• convection of the air heated by the lamp.

• radiation from the lamp to Siti.

• free electron diffusion from the lamp to Siti.

Two similarly sized metal cans have different outer casings. One is painted dull and black, and the other is painted shiny and silver. Both cans are filled with equal amounts of water and heated to the same temperature after which they are left to cool to room temperature. Which of the following statements best describes the cooling process of the water?

• Water in the dull and black can takes a shorter time to cool because dull and black surfaces are good absorbers of radiation.

• Water in the dull and black can takes a longer time to cool because dull and black surfaces are good emitters of radiation.

• Water in the shiny and silver can takes a shorter time to cool because shiny and silver surfaces are bad absorbers of radiation.

• Water in the shiny and silver can takes a longer time to cool because shiny and silver surfaces are bad emitters of radiation.

Which of the following is the best thermal insulator?

• Still air

• Wood

• Insulating plastic

• Water

Certain physical characteristics of a polar bear help it to reduce heat loss in winter. Choose the correct characteristics from the list below.

1 Its white coat reduces heat loss by radiation.

2 A layer of fat under its skin reduces heat loss by conduction.

3 The thick fur reduces heat loss by convection.

• 1 and 2 only

• 1 and 3 only

• 2 and 3 only

• All of the above

A solar panel is designed to collect heat from the Sun. Which of the following panel designs is most appropriate for this purpose?

• A black-coloured panel is used because black surfaces are better absorbers of heat.

• A light-coloured panel is used because white surfaces are better absorbers of heat.

• A black-coloured panel is used because black surfaces are better emitters of heat.

• A light-coloured panel is used because white surfaces are better emitters of heat.