6091 Chapter 9 Thermal Processes

The diagram shows a vacuum flask and an enlarged view of a section through the flask wall. The main reason for the silvering is to reduce heat transfer by

• conduction only
• conduction and convection
• radiation only
• radiation and convection

A piece of solid wax is attached at one end of a metal rod at room temperature (20 degrees celsius). The other end of the rod is placed in boiling water. After some minutes, the wax starts to melt. Which graph shows how the temperature T of the rod varies with the distance d along the rod at this time?

• A
• B
• C
• D

A house, built in a country with a hot, sunny climate, stays cool in the day. Which material for the wall and which outside colour keeps the house the coolest?

• wall material = bad conductor, outside colour = dark
• wall material = bad conductor, outside colour = light
• wall material = good conductor, outside colour = dark
• wall material = good conductor, outside colour = light

Four bars, all of exactly the same size, are each placed with one end in boiling water. The times taken for the temperature of the other end to increase by 2 0 C are measured. To make a large metal tank with the least heat loss, which materials should be used for the walls of the tank and its insulation?

• tank = aluminium, insulation = cork
• tank = aluminium, insulation = styrofoam
• tank = copper, insulation = cork
• tank = copper, insulation = styrofoam

Which surface is the best absorber of heat radiation?

• dull black
• dull white
• shiny black
• shiny white

A gas stove is used to boil some water in a metal pan. Which row describes how thermal energy is transferred through the metal pan and throughout the water?

• metal pan = conduction, water = conduction
• metal pan = conduction, water = convection
• metal pan = convection, water = conduction
• metal pan = convection, water = convection

The diagrams show four identical cans with their outside surfaces painted either dull black or polished silver. Each can contains the same volume of water, initially at 80 degrees celsius. After five minutes in a cool room, which can contains the coolest water?

• A
• B
• C
• D

A cup made from silver is filled with boiling water from a kettle. A man touches the outside surface of the cup and finds that it is extremely hot. Why is the surface so hot?

• A shiny surface is good emitter of infra-red radiation
• Boiling water gives out latent heat.
• Convection takes place in the boiling water.
• Silver is a good conductor of heat.

A beaker of water is heated at the bottom to form a convection current in the water. An explanation of the convection current contains four statements. 1 The water at the bottom becomes warmer. 2 The density of the water decreases. 3 Less dense water rises and cold water moves in to replace it. 4 Water expands.

• 1 --> 2 --> 3 --> 4
• 1 --> 3 --> 4 --> 2
• 1 --> 4 --> 2 --> 3
• 1 --> 4 --> 3 --> 2

The diagram shows a plate-warmer in which candles are used as heaters. The flames of the candles do not touch the underside of the top tray. How does heat pass to the top tray?

• mainly conduction and some convection
• mainly conduction and some radiation
• mainly convection and some radiation
• mainly radiation and some conduction