Question

Imagine that you have a metal bar sitting half in the sun and half in the dark. On a sunny day, the part of the metal that has been sitting in the sun feels hot. If you touch the part of the metal bar that has been sitting in the dark, will it feel hot or cold? Justify your answer in terms of thermal conductivity.

Short answer

The part of the metal bar that has been sitting in the dark will feel hot due to the high thermal conductivity of the metal, allowing efficient heat transfer from the sun-exposed part to the shaded part.

Step-by-step solution

Understanding Thermal Conductivity

Thermal conductivity is a measure of a material's ability to transfer heat. In this context, it indicates how effectively the heated portion of the metal bar transfers the absorbed heat from the sun to the other part of the bar in the dark. Higher thermal conductivity results in more efficient heat transfer.

Metal Bar's Properties

Most metals, like the one in this exercise, have high thermal conductivities. They can effectively and quickly transfer heat between atoms within the material due to the lattice structure of their atoms and freely moving electrons that can transfer energy. Therefore, the heat from the sunny portion of the metal bar will flow to the shady portion quite efficiently.

Temperature of the Dark Part

As the thermal conductivity of metals is typically high, the heat from the part exposed to the sun will be efficiently transferred to the portion in the dark. Consequently, the shaded part of the metal bar will also feel hot as it absorbs the heat conducted from the sun-exposed part.

Final Answer

The part of the metal bar that has been sitting in the dark will feel hot due to the high thermal conductivity of the metal, which allows efficient heat transfer from the sun-exposed part to the shaded part.