During heat transfer by conduction in solids, energy is mainly transferred from one part of the material to another when molecules or atoms do what?

Introduction / Context:
Heat can be transferred by three main mechanisms: conduction, convection and radiation. In solids, especially metals, conduction is the dominant mode of heat transfer. At the microscopic level, conduction involves interactions among particles in the material. This question asks you to identify what molecules or atoms do during conduction that allows thermal energy to be passed along.

Given Data / Assumptions:

• The heat transfer mode under consideration is conduction, primarily in solids.
• We are focusing on the microscopic behaviour of molecules or atoms.
• Options refer to collisions, chemical combination, simple heating and an open none of the above choice.
• We assume a basic kinetic theory model of matter.

Concept / Approach:
In conduction, heat is transferred within a body or between bodies in direct contact without any bulk movement of matter. In solids, atoms and molecules vibrate about their mean positions. When one end of a solid is heated, particles there vibrate more vigorously and collide with neighbouring particles, passing on some of their energy. This chain of collisions and interactions transfers energy from the hot end to the cold end. In metals, free electrons also carry energy, but collisions and interactions remain central. Thus, conduction occurs because molecules or atoms collide and interact, sharing energy. Chemical combination is not necessary, and simply being heated without interaction does not transfer energy from one region to another.

Step-by-Step Solution:
Step 1: Recall that conduction does not involve large scale movement of matter; the material stays in place. Step 2: At the hot end of a solid bar, particles gain kinetic energy and vibrate more strongly. Step 3: These energetic particles interact with neighbouring particles through collisions and intermolecular forces. Step 4: During these collisions, some of the kinetic energy is transferred from hotter particles to cooler ones. Step 5: This process repeats, sending energy step by step along the material from the hot region to the cold region. Step 6: There is no need for particles to combine chemically to transfer heat; conduction is a physical process. Step 7: Therefore, the key microscopic action in conduction is that molecules collide with neighbouring molecules and share energy.

Verification / Alternative check:
According to kinetic theory, temperature is related to average kinetic energy of particles. When a metal rod is heated at one end, experiments show that the other end gradually warms up even though metal does not flow. This can be explained by vibration and collisions of atoms and electrons transferring energy. In insulators, where electrons are less free, lattice vibrations and collisions of atoms dominate conduction. No chemical reaction takes place, and simply heating identical isolated particles would not spread energy along a solid. These observations confirm that collisions and interactions among neighbouring particles are central to conduction.

Why Other Options Are Wrong:
Combine to form new substances describes chemical reactions, not the physical process of heat conduction in a solid. Are simply heated without interaction cannot transfer energy from one region to another; interaction through collisions is necessary. None of the above is incorrect because collisions with neighbouring molecules are exactly how conduction occurs at the microscopic level.

Common Pitfalls:
Some learners mix up conduction with convection and think that particle movement is required in both cases. In conduction, particles vibrate and collide but do not undergo large scale bulk motion. Another confusion is between conduction and chemical change. Heat conduction in solids is a physical process and does not require new substances to form. Remember that in conduction, energy flows through collisions and interactions between neighbouring particles, which is why this option is correct.

Final Answer:
Heat transfer by conduction occurs when molecules collide with neighbouring molecules and transfer energy through these interactions.