Answer :
Final answer:
The vacuum in a vacuum flask prevents thermal energy transfer by conduction and convection. Heat cannot be conducted or convected due to the absence of particles in the vacuum. Radiation can still occur but is minimized by reflective coatings, making the correct answer D: Conduction and convection.
Explanation:
Understanding Thermal Energy Transfer in Vacuum Flasks
A vacuum flask, also known as a thermos, is designed to minimize heat transfer to keep beverages hot or cold. The structure of a vacuum flask consists of two layers of glass with a vacuum in between. This vacuum effectively prevents heat transfer by minimizing certain mechanisms.
Methods of Heat Transfer
There are three primary methods of thermal energy transfer:
- Conduction - the process of heat transfer through direct contact between materials.
- Convection - the transfer of heat by the movement of fluid (liquid or gas).
- Radiation - the transfer of heat through electromagnetic waves, such as infrared radiation.
In the case of a vacuum, the presence of a vacuum eliminates the medium required for conduction and convection. Since there are no particles in a vacuum, heat cannot be conducted or convected. However, radiation can still occur, although it is minimized by reflective coatings on the inner walls of the flask.
Correct Answer
Therefore, the correct answer to the question, "Which method(s) of thermal energy transfer are prevented by the vacuum?" is D. Conduction and convection. This means that conduction and convection are effectively eliminated, while radiation can still occur to an extent.
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