Question

Consider the following experimental setup in which an experimenter is heating a metal band at its center with a burner.

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Which of the following investigations correctly explains heat transfer through the metal band?

A.
Conduction transfers heat energy through the metal band. With the supply of heat energy, the closely-packed metal ions gain kinetic energy and vibrate about their mean positions. At the same time, the free electrons transfer this excessive kinetic energy from the hot end to the cold end of the metal band. Free electrons transfer the energy as they collide with ions moving through the lattice.

B.
Radiation transfers heat energy through the metal band. The metal ions in the bottom layer are in contact with the burner. The burner is at a very high temperature, and it emits thermal energy in space in the form of infrared radiation.

C.
Convection transfers heat energy through the metal band. The metal ions in contact with the heat energy from the burner gain lot of kinetic energy; therefore, they expand and move upward through the crystal to reach the surface. At the same time, the surface molecules are having less kinetic energy and are more compact, so they are pushed downward. This causes a sort of convection current in the crystal structure of the metal.

D.
Conduction and radiation transfer heat energy through the metal band. From the burner, the metal ions at the bottom of the layer receive heat energy through infrared radiation. Then, the heat energy transfers from the hot end to the cold end of the metal band by conduction.

Answer 1

A is correct.

Heat travels through the metal band by conduction: energy is passed by lattice vibrations (phonons) and — in metals — largely by mobile (free) electrons that pick up energy at the hot region and carry it to cooler regions by collisions.

Why the others are wrong:
- B: Radiation can heat the surface from the burner/flame, but it does not carry heat through the solid metal; internal transfer is conduction.
- C: Convection is a bulk motion process that occurs in fluids, not in a solid crystal lattice, so there is no convection of ions in the metal.
- D: While the burner can deliver energy to the band surface by radiation (and by hot gas convection), the claim that radiation transfers heat through the metal is incorrect — once inside the metal the dominant mechanism is conduction.