Question

two iron rods are placed horizontally, touching end-to-end. one end of one rod is heated. after some time, the other rod also feels warm to touch. how did the heat travel from the heated rod to the one that was not heated?
a the air over the heated rod traveled to the other rod and made it warm.

b part of the heat was converted to radiation and traveled to the cooler rod.

c electrons within the rods started moving, distributing heat consistently in both rods.

d the molecular movement in the first rod transferred energy to the molecules in the second.

Explanation:

• Option A: Air doesn't travel to transfer heat here; heat transfer between the rods is through contact, not air movement. Eliminate A.
• Option B: Radiation is heat transfer via electromagnetic waves, but here the rods are in contact, so conduction (not mainly radiation) is the key. Eliminate B.
• Option C: In metals, heat transfer is via lattice vibrations and free electrons, but the description of electrons "distributing heat consistently" is inaccurate. Heat transfer in solids (conduction) is due to molecular/atomic vibrations transferring energy, not just electron movement in this simplistic way. Eliminate C.
• Option D: When one rod is heated, the molecules vibrate more. Through conduction (since the rods are in contact), the molecular movement (vibrations) in the first rod transfers energy (heat) to the molecules in the second rod, causing it to warm up. This matches the concept of heat conduction in solids.

Answer:

D. The molecular movement in the first rod transferred energy to the molecules in the second.