The question asks about the specific role of the reflective coating in a thermos flask in preventing heat transfer. A thermos flask is designed to minimize all three modes of heat transfer: conduction, convection, and radiation. Each component of the flask targets a specific mode of heat transfer. We need to identify which mode is primarily addressed by the reflective coating.
Correct Option: C) Radiation. The reflective coating (often silvering) on the inner and outer surfaces of the vacuum bottle is specifically designed to minimize heat transfer by radiation. It reflects infrared radiation, preventing heat from radiating into or out of the flask.
The question asks for the original name of the thermos flask. This is a factual recall question related to the history of scientific inventions. We need to identify the historical name given to this device by its inventor.
Therefore, the original name, particularly in scientific contexts and after its inventor, was Dewar Flask.
B) Dewar Flask — This is the original name given to the vacuum flask, named after its inventor, Sir James Dewar.
The question asks about the material used for the stopper or cap of a thermos flask to ensure a tight seal. The primary function of a thermos flask is to minimize heat transfer (conduction, convection, radiation) between its contents and the surroundings. A tight seal is crucial to prevent heat loss or gain through convection and evaporation. We need to consider the properties of different materials in this context.
Correct Option: B) Rubber or Plastic — These materials are excellent insulators and are flexible, allowing them to form a tight, air-proof seal that prevents heat transfer by convection and evaporation, which is crucial for maintaining the temperature of the contents in a thermos flask.
The question asks about the factor that least influences the effectiveness of a thermos flask in retaining heat. We need to analyze how each given option relates to the principles of heat transfer (conduction, convection, radiation) and the design of a thermos flask.
Correct Option: C) The thickness of the walls. The vacuum layer and reflective surfaces are the main barriers to heat transfer in a thermos flask. While wall thickness does play a role in conduction, its influence is minimal compared to the effectiveness of the vacuum and the material's insulating properties.
The question asks about the primary function of a thermos flask. A thermos flask is designed to maintain the temperature of its contents, whether hot or cold, for an extended period. This function is achieved by minimizing heat transfer between the contents and the surroundings.
Correct Option: B) Reduces heat loss or gain. This option accurately describes the primary mechanism by which a thermos flask maintains the temperature of its contents. It does not actively heat or cool but rather insulates to prevent temperature changes.
The question asks to identify which option is NOT a common use for a thermos flask. A thermos flask, also known as a vacuum flask, is designed to minimize heat transfer (conduction, convection, and radiation) to keep its contents at a stable temperature for an extended period. We need to evaluate each option based on this primary function.
B) Storing ice cream — While a thermos flask can slow down the melting of ice cream, it is not its common or intended use for effective storage. Ice cream requires much colder temperatures than a standard thermos can maintain for practical durations, especially compared to its effectiveness with hot liquids or cryogenic substances.