The electrical conductivity of a metal is directly proportional to the number of free electrons present. More free electrons mean a greater ability for the metal to conduct electricity. This is because a higher concentration of free electrons provides more charge carriers to contribute to the electric current when a potential difference is applied.

Different metals have different numbers of free electrons due to their atomic structure and the number of valence electrons available for delocalisation. Metals with fewer valence electrons or those where the electrons are more tightly bound to the atoms will have fewer free electrons and therefore lower conductivity. For example, copper and silver have a high number of free electrons and are excellent conductors, while materials like insulators (e.g., rubber, glass) have very few free electrons and are poor conductors. The ease with which electrons can move through the metal lattice also plays a role; metals with a more regular and less disrupted lattice structure generally exhibit higher conductivity.

When a metal bar is heated at one end, the particles within the heated region gain kinetic energy and vibrate more vigorously. These vibrating particles then collide with neighbouring particles, transferring some of their kinetic energy. This process continues as the vibrations are passed on through the metal lattice, causing the temperature to rise progressively along the bar. The heat energy essentially propagates through the metal as a wave of vibrating particles.

Metals are good conductors of heat due to their unique atomic structure and the presence of free electrons. Metals have a metallic bonding structure where valence electrons are delocalised and free to move throughout the entire metal lattice. These free electrons can readily absorb kinetic energy from the vibrating particles in the hotter region and transport it to cooler regions.

This mechanism of heat transfer, involving the movement of free electrons, is much more efficient than the vibration-based heat transfer in non-metals. The high mobility of electrons allows for rapid and effective heat propagation throughout the metal, making metals excellent conductors of heat. The more free electrons a metal has, the better its thermal conductivity will be.

(a) The metal is the best thermal conductor and the wood is the poorest thermal conductor (the best thermal insulator). Explanation: In a good thermal conductor (like metal), the particles (atoms and electrons) are arranged in a way that allows heat energy to be transferred efficiently through vibrations and collisions. This is due to the free electrons in metals. In a poor thermal conductor (like wood), the particles are arranged in a more disordered way, and there are fewer free electrons to facilitate heat transfer. This means heat energy is not transferred as efficiently.

(b) One improvement would be to ensure the blocks are of the same thickness and have the same cross-sectional area. This would eliminate any variations in heat transfer due to differences in size and shape. Also, ensuring the hot plate is at the same distance from the surface of each block would improve the consistency of the heat input.