A physicist is demonstrating the concept of specific heat capacity. She places two identical blocks, one aluminum and one iron, on a hot plate. After five minutes, the aluminum block feels significantly hotter than the iron block. Assuming both blocks started at the same temperature and received the same amount of heat, what does this observation imply?
- AIron has a higher specific heat capacity than aluminum.
- BAluminum has a higher specific heat capacity than iron.
- CAluminum has a higher thermal conductivity than iron.
- DIron has a lower density than aluminum.
Show answer & explanationAnswer & explanation
Correct answer: A. Iron has a higher specific heat capacity than aluminum.
Specific heat capacity is the amount of heat energy required to raise the temperature of a substance by a certain amount. If aluminum heats up more quickly (feels significantly hotter) than iron when both receive the same amount of heat, it means aluminum requires less heat to change its temperature, thus iron has a higher specific heat capacity. (Specific heat of Aluminum ≈ 0.90 J/g°C; Iron ≈ 0.45 J/g°C. The question implies the opposite, that aluminum heats faster, so iron must have a higher specific heat if the observation is correct. Wait, the premise states aluminum 'feels significantly hotter' meaning it *rose* in temperature more. If it rose in temperature more for the same heat input, it has a *lower* specific heat capacity. Therefore, iron must have a higher specific heat capacity. The question is tricky because it's about what the observation *implies* about iron, not aluminum directly. Let's re-read. 'aluminum block feels significantly hotter than the iron block.' This implies ΔT_Al > ΔT_Fe. Since Q = mcΔT, and Q and m are similar (identical blocks implies identical mass), then for ΔT_Al > ΔT_Fe, c_Al must be < c_Fe. So, iron has a higher specific heat capacity than aluminum. This makes sense. Water has a very high specific heat capacity, so it takes a lot of energy to heat it up, but it holds heat well. Iron would take more energy to heat up than aluminum, so if aluminum is hotter, iron is 'resisting' temperature change more. So, B is correct.
Why the other options are wrong
- B. If aluminum feels hotter, it means its temperature increased more. A larger temperature increase for the same heat input implies a *lower* specific heat capacity for aluminum.
- C. Thermal conductivity affects how quickly heat *transfers through* the material, not primarily how much its temperature *changes* for a given heat input.
- D. Density is mass per unit volume; while relevant, it doesn't directly explain the temperature difference for equal heat input the way specific heat capacity does.
Specific Heat Capacity (c)
The amount of heat energy required to raise the temperature of a unit mass of a substance by one degree Celsius (or Kelvin).
- Units are typically J/(g·°C) or J/(kg·K).
- Materials with high specific heat capacity resist changes in temperature.
- Water has a very high specific heat capacity (4.18 J/g°C).
Memory trick: Specific heat resists the heat, Conductivity lets it flow with speed.