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Class 7 Science — Heat transfer in nature

Tell conduction, convection and radiation apart by what the particles do, explain land and sea breezes, and follow water from the sea to an aquifer.

Name: ________________________

Before you start

Four pins are stuck along a metal strip with wax, and one end of the strip is heated. Here is the strip, pin by pin.

1234
  1. 1. Pin I
  2. 2. Pin II
  3. 3. Pin III
  4. 4. Pin IV

The heat travels along the strip from the heated end towards the cold one, melting each blob of wax as it arrives. Pin I sits nearest the flame and Pin IV farthest away, so the pins drop one after another in that order. The strip itself has not moved anywhere — just the heat has.

  1. 1.Groundwater levels in many towns are falling. Which pair of causes does the chapter give?

    • a) Too much rainwater harvesting, and too many recharge pits
    • b) Rainfall stopping altogether, and rivers changing course
    • c) Aquifers turning to solid rock, and wells being dug too shallow
    • d) Heavy extraction for a growing population, and concrete surfaces that leave less room for water to soak in

  2. 2.Match each way of transferring heat to what the particles are doing.

    • Conduction
    • Convection
    • Radiation
    • the heated particles themselves move, carrying the heat
    • heat passes along, and the particles stay where they are
    • heat crosses with no medium to carry it

  3. 3.The same amount of water is poured through one bottle of clay, one of sand and one of gravel. Through which does it come out fastest, and why?

    • a) Clay, because its particles are the smallest and pack loosely
    • b) They finish together, because the same water was poured into each
    • c) Sand, because it is the driest of the three
    • d) Gravel, because the spaces between its particles are the widest

  4. 4.Convection in a beaker turns round and round with no true beginning, so start from the step where water at the bottom is heated by the flame and put the rest in order.

    • Cooler, heavier water sinks down the sides to take its place
    • The heated water expands and becomes lighter
    • Water at the bottom is heated by the flame
    • That lighter water rises up through the middle

  5. 5.Which of the three ways of transferring heat can cross a space with nothing in it?

    • a) Conduction
    • b) Conduction and convection both
    • c) Convection
    • d) Radiation

  6. 6.An underground layer of sediment and rock that holds water in its pore spaces, and that a bore well is drilled into, has a name. What is it?

  7. 7.Sort each material by how readily it lets heat pass through.

    Groups: Good conductor of heat · Poor conductor of heat

    • Aluminium
    • Steel
    • Wood
    • Glass
    • Air
    • Clay

  8. 8.Why is light-coloured clothing more comfortable in summer?

    • a) It is made of thinner cloth than dark clothing is
    • b) It reflects most of the heat falling on it, while dark surfaces absorb more
    • c) It lets sweat evaporate faster than dark cloth does
    • d) It conducts heat away from the body faster than dark cloth

Answer key — Class 7 Science — Heat transfer in nature

  1. 1. d) Heavy extraction for a growing population, and concrete surfaces that leave less room for water to soak in
  2. 2. Conduction → heat passes along, and the particles stay where they are; Convection → the heated particles themselves move, carrying the heat; Radiation → heat crosses with no medium to carry it
  3. 3. d) Gravel, because the spaces between its particles are the widest
  4. 4. 1. Water at the bottom is heated by the flame 2. The heated water expands and becomes lighter 3. That lighter water rises up through the middle 4. Cooler, heavier water sinks down the sides to take its place
  5. 5. d) Radiation
  6. 6.
    • aquifer
    • an aquifer
    • aquifers
  7. 7. Steel → Good conductor of heat; Aluminium → Good conductor of heat; Wood → Poor conductor of heat; Glass → Poor conductor of heat; Clay → Poor conductor of heat; Air → Poor conductor of heat
  8. 8. b) It reflects most of the heat falling on it, while dark surfaces absorb more