heat energy (2)

The transfer of heat which does not need any material medium is by.................

• conduction.

• radiation.

•  convection.

In solar cells, the solar energy is converted into heat energy. ( )

• true

• false

In the electric iron, electric energy is changed into heat energy. ( )

• true

• false

The Sun is a permanent resource of energy. while electricity is a non-renewable resource of energy. ( )

• false

• true

Cool air rises up, but hot air falls down. ( )

• true

• false

Heat transfer by radiation takes place through 

• liquids only.

• gases only.

• metals only.

• material media and non-material ones.

Which of the following devices pollutes the environment ? 

• Electric oven.

• Electric heater.

• Gas oven.

• All the previous devices.

The mechanical energy is converted into heat energy by ............

• the electric generator (dynamo).

• the water heater.

• friction of movement objects.

• the electric motor.

 The Sun is ...........

•  a resource of permanent energy.

• not an energy resource.

• a resource of non-permanent energy.

• producing no energy.

In solar heater, the solar energy is converted into  

• light

• heat

• kinetic