Thermal Energy & Heat Transfer — Drills · Grade 8 Science

Chapter: Energy & Heat Transfer

What these drills covers

By the end of Thermal Energy & Heat Transfer you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: thermal energy, heat, conduction, convection, radiation, thermal equilibrium, model, evidence, system boundary, assumption.

Problem 1

Heat transfer through direct contact between particles is
  1. conduction
  2. convection
  3. radiation
  4. evaporation
Answer and explanation

conduction

Conduction passes energy particle to particle without the material itself flowing.

Problem 2

Warm air rising above a heater is
  1. conduction
  2. convection
  3. radiation
  4. insulation
Answer and explanation

convection

Convection moves energy by the bulk movement of a fluid.

Problem 3

Energy reaching Earth from the Sun travels by
  1. conduction
  2. convection
  3. radiation
  4. all three equally
Answer and explanation

radiation

Radiation needs no medium, which is why it crosses the vacuum of space.

Problem 4

Metals feel colder than wood at the same room temperature because metals
  1. are colder
  2. conduct heat away from your hand faster
  3. have more mass
  4. radiate more
Answer and explanation

conduct heat away from your hand faster

Both are at room temperature; the metal removes energy from your skin faster, which your hand reads as cold.

Problem 5

Water at 80 °C is mixed with an equal mass at 20 °C, with no losses. What is the final temperature in °C?
Answer and explanation

50 °C

Equal masses of the same substance settle midway: (80 + 20)/2 = 50 °C.

Problem 6

Thermal energy always flows from
  1. cold to hot
  2. hot to cold
  3. large to small
  4. solid to liquid
Answer and explanation

hot to cold

Net transfer is from higher to lower temperature until they are equal.

Problem 7

Explain the difference between temperature and thermal energy using a cup and a bath of water at the same temperature.
Answer and explanation

Temperature measures the average kinetic energy of the particles, which is the same in both. Thermal energy is the total energy of all the particles, and the bath has vastly more because it contains far more particles. This is why the bath can warm a cold room noticeably while the cup cannot, despite the identical thermometer reading.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Explain how a vacuum flask reduces all three forms of heat transfer.
Answer and explanation

The vacuum between its walls removes the particles needed for conduction and convection, so neither can carry energy across the gap. The silvered surfaces reflect radiation back toward the contents rather than absorbing and re-emitting it outward. The stopper limits convection at the top, where hot liquid would otherwise carry energy out. Each feature targets a different mechanism, which is why the combination works.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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