1.1 Difference in Thermal Energy Conduction
Non-metallic rod:
- Non-metallic materials (such as wood or plastic) are generally poor conductors of heat. This is because they lack free electrons that can move easily through the material to transfer thermal energy. Instead, heat conduction occurs primarily through vibrational energy transfer between neighboring molecules, which is relatively slow.
Metallic rod:
- Metallic materials (such as copper or aluminum) are excellent conductors of heat due to the presence of free electrons. These electrons can move freely throughout the material, allowing them to carry thermal energy quickly from one part of the rod to another. Additionally, metallic bonds facilitate fast energy transfer by enabling vibrations of atoms that further enhance thermal conduction.
1.2 Features of a Thermos Flask
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Vacuum between the inner and outer walls
- Method of heat transfer prevented: Conduction and convection
- Explanation: The vacuum eliminates any air (and thus reduces conduction and convection), which are necessary for these methods of heat transfer. Since there are no molecules in the vacuum to conduct heat, this feature significantly slows down heat transfer.
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Reflective coating on the inner surface
- Method of heat transfer prevented: Radiation
- Explanation: The reflective coating (often made of silver) reflects infrared radiation back into the flask. This prevents heat energy from escaping the contents through radiation, thus maintaining the temperature of the beverage inside.
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Tightly sealed cork or plastic stopper
- Method of heat transfer prevented: Convection and conduction
- Explanation: A tightly sealed stopper minimizes the air exchange between the inside and outside of the flask. This further reduces heat transfer by limiting the amount of air that can carry away or bring in thermal energy through conduction and convection processes.
1.3 Boiling Point of Water at Different Altitudes
The boiling point of pure water decreases at higher altitudes due to a reduction in atmospheric pressure. At lower altitudes, the atmospheric pressure is higher, which means that it takes more energy (heat) for water molecules to escape into the vapor phase, resulting in a higher boiling point. Conversely, at higher altitudes, the lower atmospheric pressure allows water molecules to escape into the vapor phase more easily, thus requiring less thermal energy, which lowers the boiling point.
1.4.1 Molecular Interpretation of Latent Heat
Latent heat refers to the energy absorbed or released by a substance during a phase change (such as melting or boiling) without a change in temperature. At the molecular level, during melting or boiling, energy is used to overcome intermolecular forces rather than increase molecular kinetic energy. For example, in the melting process, the heat energy provided is used to break the structured arrangement of molecules in a solid, allowing them to move more freely in a liquid state, while the temperature remains constant throughout the phase transition.
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