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Heat and temperature

Ten questions of mixed difficulty, covering Heat and temperature. Print it, or work through it on screen — the answer key starts on its own page.

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Heat and temperature

Science 7 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. A metal spoon and a wooden spoon stand in the same pot of hot soup. After a minute, the metal handle feels much hotter. This is because metal

    1. a) was hotter than wood to begin with
    2. b) is a good conductor of heat
    3. c) is a good insulator of heat
    4. d) makes its own heat once it is warm

  2. On a warm day, droplets form on the outside of a glass of iced lemonade. This change of state is

    1. a) sublimation
    2. b) evaporation
    3. c) condensation
    4. d) melting

  3. Which of these energy sources is renewable?

    1. a) Wind
    2. b) Coal
    3. c) Oil
    4. d) Natural gas

  4. Some people say turning the thermostat down at night saves nothing, because the furnace must warm the house up again in the morning. Why does it still save energy?

    1. a) A cooler house loses heat to the cold outdoors more slowly
    2. b) A furnace burns its fuel more efficiently at night
    3. c) Heat flows into the house from outside overnight
    4. d) Cold air holds more thermal energy than warm air does

  5. A bimetallic strip is a strip of brass bonded to a strip of steel. When heated, brass expands more than steel does. What happens when the strip is heated?

    1. a) It shrinks, as the two metals pull against each other
    2. b) It stays straight and just gets a little longer
    3. c) It bends, with the steel on the outside of the curve
    4. d) It bends, with the brass on the outside of the curve

  6. A bathtub holds water at 40 °C, and a mug holds water at 80 °C. Which statement is correct?

    1. a) Both hold the same thermal energy, because both are just water
    2. b) The bathtub's particles move faster, because it holds more water
    3. c) The mug's particles move faster, but the bathtub holds more thermal energy
    4. d) The mug holds more thermal energy, because its water is hotter

  7. A student heats crushed ice and records the temperature every minute: −10, −5, 0, 0, 0, 0, 5, 10 °C. Why does the temperature stay at 0 °C for four readings?

    1. a) The ice gives off heat as it melts, cancelling the burner
    2. b) The burner gave out less energy while those readings were taken
    3. c) A thermometer cannot measure the temperature of melting ice
    4. d) The energy is going into melting the ice, not warming it

  8. Electric heaters in a room are usually placed low down, near the floor, rather than near the ceiling. Why does this warm the room better?

    1. a) A heater gives off radiation only when it is close to the floor
    2. b) The floor is a good conductor, so it spreads the heat to every wall
    3. c) Cold air is lighter than warm air, so it gathers near the ceiling
    4. d) Warm air rises and cool air sinks, so heat circulates through the room

  9. On a cold, clear winter day, you feel the Sun warm your face even though the air around you is cold. The energy reaches you mainly by

    1. a) convection
    2. b) conduction
    3. c) radiation
    4. d) evaporation

  10. Four identical cans of water at 80 °C are left for 20 minutes, three of them wrapped. Final temperatures: foil, 62 °C; cotton, 66 °C; wool, 70 °C; no wrap, 60 °C. Which was the best insulator?

    1. a) Wool, because its water cooled the least
    2. b) Foil, because shiny metal keeps heat in
    3. c) None, because every can still lost heat
    4. d) No wrap, because its water changed the most

Answer key · Heat and temperature

Science 7 · maddyhelps.com

  1. b) is a good conductor of heat — Metal conducts heat well, passing energy quickly from particle to particle up the handle. Wood is an insulator, so its handle stays cool; both spoons started at the same room temperature.
  2. c) condensation — Water vapour in the air loses energy when it touches the cold glass and turns to liquid, which is condensation. The drops did not leak through the glass: they form on a sealed can of pop too, and their water came from the air.
  3. a) Wind — A renewable source is replaced naturally as fast as we use it, and the wind keeps blowing because the Sun keeps heating the air unevenly. Coal, oil and natural gas formed from ancient living things over millions of years, so what we burn is gone for good on any time scale that matters to us.
  4. a) A cooler house loses heat to the cold outdoors more slowly — Heat leaks out faster when the difference between inside and outside is bigger, so a house kept cooler overnight loses less energy in total, even counting the morning warm-up. The furnace only ever replaces heat that has leaked away, so less leaking means less fuel.
  5. d) It bends, with the brass on the outside of the curve — The brass grows longer than the steel it is stuck to, so the strip has to curve, and the longer metal ends up on the outside of the bend. A thermostat uses this bending to open or close a switch as a room warms and cools.
  6. c) The mug's particles move faster, but the bathtub holds more thermal energy — Temperature is the average motion of the particles, so the hotter mug wins on that. But the bathtub has vastly more particles, and adding up all of their energy gives far more in total, which is why a tub of warm water can melt far more snow than a mug of hot water.
  7. d) The energy is going into melting the ice, not warming it — While ice melts, the energy goes into freeing particles from their fixed places rather than making them move faster, so the temperature holds level until all the ice has melted. The burner is adding energy the whole time; a flat part on a heating graph means a change of state, not a pause in heating.
  8. d) Warm air rises and cool air sinks, so heat circulates through the room — Air warmed by the heater expands, becomes less dense and rises, and cooler air sinks to take its place, setting up a convection current that carries heat around the room. A heater near the ceiling would leave a layer of warm air trapped up there and the floor cold.
  9. c) radiation — Radiation carries energy as waves that need no particles, which is how sunlight crosses empty space to reach Earth. Conduction and convection both need matter to carry the energy, and the cold air around you is clearly not what is warming your face.
  10. a) Wool, because its water cooled the least — An insulator slows the transfer of heat, so the best one leaves the water warmest: the wool can dropped only 80 − 70 = 10 °C, against 20 °C with no wrap. Foil is a metal, a good conductor, and it helped least; no insulator stops heat completely, it only slows it down.