Expression of IdeasMediumExplaining how something works
Expression of Ideas practice question
While researching a topic, a student has taken the following notes:
- A thermos flask has two walls of glass or steel with a vacuum between them.
- Heat cannot travel by conduction or convection through a vacuum.
- The inner surfaces are silvered to reflect radiant heat.
- The flask keeps drinks hot or cold for hours.
The student wants to explain why a thermos flask keeps drinks hot. Which choice most effectively uses relevant information from the notes to accomplish this goal?
- A. The vacuum between the flask's two walls blocks heat transfer by conduction and convection, and the silvered surfaces reflect radiant heat back.Correct
- B. A thermos flask has two walls.
- C. A thermos keeps drinks hot for hours.
- D. Glass and steel are used in flasks.
Answer: A. The vacuum between the flask's two walls blocks heat transfer by conduction and convection, and the silvered surfaces reflect radiant heat back.
Vacuum and silvering, each with its role.
Why the other answers are wrong
- B. A thermos flask has two walls.
- The structure without the mechanism.
- C. A thermos keeps drinks hot for hours.
- Restates the effect, doesn't explain it.
- D. Glass and steel are used in flasks.
- Materials alone.
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