Science 9 · Unit 3: Forces and energy · Cambridge Lower Secondary Science Stage 9

Questions

1. 1. When air is heated, why does it rise?

   • Its particles get bigger.
   • Its particles get lighter.
   • Heat pulls it upwards.
   • Its particles move faster and spread out, so the air becomes less dense.
   Check

2. 2. A vacuum flask has a vacuum between two walls. Which transfers does the vacuum stop?

   • conduction only
   • radiation only
   • conduction and convection
   • all three
   Check

3. 3. Inside a vacuum flask there is a glass bottle with a silver surface. How does the silver surface help keep a drink hot?

   • It is a good conductor of thermal energy.
   • It reflects thermal radiation back towards the drink.
   • It absorbs thermal radiation from the drink.
   • It sets up convection currents in the drink.
   Check

4. 4. Which surface is the best absorber of thermal radiation?

   • dull white
   • shiny white
   • dull black
   • shiny silver
   Check

5. 5. How does thermal energy reach the Earth from the Sun?

   • convection
   • conduction
   • radiation
   • evaporation
   Check

6. 6. How is thermal energy transferred through a metal bar?

   • convection
   • conduction
   • evaporation
   • radiation
   Check

7. 7. When warm air rises through cold air, what is this called?

   • conduction
   • radiation
   • insulation
   • convection
   Check

8. 8. Which TWO types of thermal energy transfer cannot happen in a vacuum?

   • conduction and convection
   • conduction and radiation
   • all three
   • convection and radiation
   Check

9. 9. Match each type of thermal energy transfer with how it works.

   • conduction
   • convection
   • radiation

   • a wave that does not need particles to carry the energy
   • heated particles spread out, the substance becomes less dense and rises
   • particles vibrate more and collide with neighbours, making them vibrate more too
   Check

10. 10. Why does conduction happen more easily in solids than in gases?

    • The particles in a solid are close together, so they easily pass vibrations to their neighbours.
    • Gas particles don't move.
    • Solids have no particles.
    • The particles in a gas are close together.
    Check

11. 11. Why can convection happen in liquids and gases but not in solids?

    • Solids are less dense than liquids.
    • Solids are too hot for convection.
    • The particles in liquids and gases can move from place to place, but in a solid they are fixed.
    • Liquids and gases have no particles.
    Check

12. 12. Why can radiation travel through a vacuum when conduction and convection can't?

    • Radiation is faster than the others.
    • A vacuum is very hot.
    • Radiation travels through the particles in a vacuum.
    • Radiation is a wave and doesn't need particles; the other two do.
    Check

13. 13. Why are cooking pots made of metal?

    • Metals are light.
    • Metals reflect the heat away from the food.
    • Metals are good conductors, so thermal energy passes quickly to the food.
    • Metals are good insulators.
    Check

14. 14. Why do cooking pots often have wooden or plastic handles?

    • They make the pot heat up faster.
    • They radiate heat away.
    • They are good conductors.
    • Wood and plastic are poor conductors (insulators), so the handle stays cool.
    Check

15. 15. Why are houses in hot countries often painted white?

    • White surfaces reflect radiation, so the house absorbs less thermal energy from the Sun.
    • White surfaces absorb more radiation.
    • White paint is a good conductor.
    • White paint stops convection.
    Check

16. 16. Why does a wool jumper help keep you warm?

    • Wool is a good conductor.
    • It traps air, which is a poor conductor, so less thermal energy leaves your body.
    • Wool makes its own heat.
    • Wool lets cold air in.
    Check

17. 17. A plastic food box is lined inside with shiny aluminium foil. How does this help to keep hot food hot?

    • The shiny foil reflects thermal radiation back towards the food, and the plastic is a poor conductor.
    • The foil is a good conductor, so it carries heat into the food.
    • The foil makes convection currents inside the box.
    • The foil absorbs radiation and passes it outside.
    Check