Year 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.

1. Pin I
2. Pin II
3. Pin III
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.Match each way of transferring heat to what the particles are doing.
- Conduction
- Convection
- Radiation
- heat crosses with no medium to carry it
- the heated particles themselves move, carrying the heat
- heat passes along, and the particles stay where they are
2.Match each breeze to what it is and when it blows.
- Sea breeze
- Land breeze
- cooler air moving from the land to the sea, by night
- cooler air moving from the sea to the land, by day
3.The seeping of surface water down through soil and rock has a one-word name in this chapter. What is it?
4.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) Sand, because it is the driest of the three
- c) They finish together, because the same water was poured into each
- d) Gravel, because the spaces between its particles are the widest
5.Groundwater levels in many towns are falling. Which pair of causes does the chapter give?
- a) Heavy extraction for a growing population, and concrete surfaces that leave less room for water to soak in
- b) Aquifers turning to solid rock, and wells being dug too shallow
- c) Rainfall stopping altogether, and rivers changing course
- d) Too much rainwater harvesting, and too many recharge pits
6.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
7.Two thin blankets keep you warmer than one thick one. What does the chapter give as the reason?
- a) Air is trapped between them, and air is a poor conductor of heat
- b) The outer blanket reflects heat back through the inner one
- c) Two blankets weigh more, and weight holds heat in
- d) Thin cloth is woven more tightly than thick cloth
8.Why is light-coloured clothing more comfortable in summer?
- a) It conducts heat away from the body faster than dark cloth
- 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 is made of thinner cloth than dark clothing is

Answer key — Year 7 Science — Heat transfer in nature

1. 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
2. Sea breeze → cooler air moving from the sea to the land, by day; Land breeze → cooler air moving from the land to the sea, by night
3. infiltration
4. d) Gravel, because the spaces between its particles are the widest
5. a) Heavy extraction for a growing population, and concrete surfaces that leave less room for water to soak in
6. 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
7. a) Air is trapped between them, and air is a poor conductor of heat
8. b) It reflects most of the heat falling on it, while dark surfaces absorb more