Students were investigating heat transfer by conduction and they set up the simple experiment you see here. Three spoons made of different materials were placed in a pot of hot (90°C) water. A pat of butter was placed on the handle of each spoon. Students were asked to predict the order of melting butter on the three spoons, from first to last. Which answer seems the most reasonable?
Responses
A plastic – wood – tinplastic – wood – tin
B plastic – tin – woodplastic – tin – wood
C wood – tin – plasticwood – tin – plastic
D tin- plastic – wood
The correct Answer and Explanation is:
The correct answer is D: tin – plastic – wood.
Explanation
Heat transfer by conduction is the process where thermal energy moves through materials via direct contact. The rate at which heat is conducted depends on the thermal conductivity of the materials involved. In this experiment, three different spoon materials (tin, plastic, and wood) are used to determine how quickly the butter melts on their handles when placed in hot water at 90°C.
1. Thermal Conductivity of Materials:
- Tin: As a metal, tin has a high thermal conductivity, meaning it can transfer heat efficiently. When the handle of the tin spoon is submerged in hot water, the heat will quickly move along the spoon, causing the butter on the handle to melt first.
- Plastic: Plastic has a relatively low thermal conductivity compared to metals. While it can conduct some heat, it does so much more slowly than tin. Therefore, the butter on the plastic spoon will melt after that of the tin spoon but before the wood.
- Wood: Wood is an excellent insulator with very low thermal conductivity. This means it does not transfer heat well, resulting in the butter melting the slowest on the wooden spoon.
2. Expected Order of Melting: Given these properties, the order of melting butter on the spoons can be predicted as follows:
- First: The butter on the tin spoon will melt first due to its high thermal conductivity, allowing it to transfer heat from the hot water to the butter effectively.
- Second: The butter on the plastic spoon will melt next as it conducts heat better than wood, though not as efficiently as metal.
- Third: The butter on the wooden spoon will melt last, as it conducts heat poorly, keeping the butter relatively cool compared to the other spoons.
Thus, the most reasonable prediction for the order of melting butter is tin (first), plastic (second), and wood (last), making D: tin – plastic – wood the correct choice. This understanding of material properties and their effect on heat transfer is crucial in thermodynamics and has practical implications in everyday life.