Fig. 24.1 shows two spoons, one made of metal and one made of wood, placed in a cup of hot water. (a) State which spoon will feel hotter at the handle end a...

(a) Which spoon feels hotter at the handle end? [1]

The metal spoon [1].

(b) Explanation in terms of thermal conduction [2]

Metal is a good conductor of thermal energy [1]. Heat is transferred from the hot water along the metal spoon to the handle much more quickly than along the wooden spoon, which is a poor conductor (insulator) [1].

The metal spoon transmits the thermal energy efficiently from the submerged end to the handle, making the handle noticeably warm. The wooden spoon blocks this transfer, so its handle stays close to room temperature.

(c) Particle-level explanation of energy transfer along the metal spoon [2]

Atoms at the hot end of the spoon (in the water) vibrate with greater amplitude. They collide with neighbouring atoms and pass on kinetic energy through these vibrations [1]. In addition, metals contain free (delocalised) electrons that gain kinetic energy at the hot end and move rapidly towards the cooler handle end, transferring energy much faster than lattice vibrations alone [1].

This free-electron mechanism is why metals are far better conductors than non-metals like wood or plastic, which lack free electrons.

(d) Why a wooden spoon is better for stirring hot food [1]

Wood is a poor conductor, so the handle stays cool and does not burn the hand [1].

(e) Another good thermal insulator and its use [1]

Plastic, used for saucepan handles (or fibreglass, used for loft insulation; or trapped air, used in double glazing) [1].

Any correct pairing of an insulating material with a sensible practical application is accepted.