10 Transfer of Thermal Energy 23 22J 22N [EUT]

A student has two blocks of metal, X and Y. The temperature of X is 50°C and the temperature of Y is 0°C. The two blocks are placed in contact with each other, as shown. After some time, both blocks have a temperature of 25°C. What has happened to the internal energy of X and Y ?

• decreased, decreased

• decreased, increased

• increased, decreased

• unchanged, unchanged

The diagram shows the view of a room heated by a radiator. The arrowed line from X to Y is the path of the convection current in the air. Which row about the air temperature and the air density at X and at Y is correct?

• Air temperature higher at X, air density higher at X

• Air temperature higher at X, air density higher at Y

• Air temperature higher at Y, air density higher at Y

• Air temperature higher at Y, air density higher at X

A room is heated by a radiator. The diagrams X and Y show two possible circulations of hot air, which heat the room. Which diagram and reason explain the heating of the room by convection?

• X - air density decreases when air is heated

• X - air density increases when air is heated

• Y - air density decreases when air is heated

• Y - air density increases when air is heated

A cupboard is placed in front of a heater. Air can move through a gap under the cupboard. Which row describes the temperature and the direction of movement of the air in the gap?

• cool - away from the heater

• cool - towards the heater

• warm - away from the heater

• warm - towards the heater

A teacher puts some cold water in a test-tube. She holds the bottom of the test-tube while heating the top. The water at the top boils but she continues to hold the test-tube as the bottom remains cold. Which conclusion about water is made from this experiment?

• Water is a bad conductor.

• Water is a bad convector.

• Water is a good conductor.

• Water is a good convector.

The diagram shows a flask designed to reduce the loss of thermal energy from a hot liquid. Which methods of thermal energy transfer are the silvered walls designed to reduce?

• conduction, convection and radiation

• conduction and convection only

• conduction only

• radiation only

Some hot water is sealed inside a metal can. The can is in a vacuum in outer space. The hot water slowly cools down. How does the thermal energy escape into space?

• by conduction then convection

• by conduction then radiation

• by evaporation then convection

• by evaporation then radiation

Four cups A, B, C and D contain hot coffee. Which cup keeps the coffee warm the longest?

• A

• B

• C

• D

Two otherwise identical cars, one black and one white, are at the same initial temperature. The cars are left in bright sunshine and their temperatures increase. During the night, their temperatures decrease. Which car shows the greater rate of temperature increase and which car shows the greater rate of temperature decrease?

• black, black

• black, white

• white, black

• white, white

Four thermometers, with their bulbs painted different colours, are placed at equal distances from a radiant heater. Which thermometer shows the slowest temperature rise when the heater is first switched on?

• dull black

• dull white

• shiny black

• shiny white