Let's analyze each statement: A) Any energy transfer that does not involve temperature difference in some way is not heat: This statement is correct. Heat is defined as energy transferred from a hotter object to a colder object due to a temperature difference. Energy can also be transferred as work (e.g., mechanical work), which does not require a temperature difference. Therefore, energy transfer that doesn't involve a temperature difference is not heat. B) Any energy transfer always requires a temperature difference: This is incorrect. Energy can be transferred as work (mechanical, electrical, etc.), which does not require a temperature difference. C) On heating the length and volume of the object remain exactly the same: This is incorrect. When most objects are heated, they undergo thermal expansion, meaning their length, area, and volume increase (though some exceptions exist like water between 0°C and 4°C). D) Whenever there is a temperature difference, heat is the only way of energy transfer: This is incorrect. While a temperature difference causes heat transfer (conduction, convection, radiation), other forms of energy transfer, such as work done on or by the system, can also occur simultaneously, even if there is a temperature difference.
Which one of the following statements is correct ?
Asked in UPSC NDA 1 2018 · Topic: Heat and Thermodynamics (Zeroth and First Laws of Thermodynamics (Internal Energy, Work, Heat, Enthalpy))
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Answer: A. Any energy transfer that does not involve temperature difference in some way is not heat
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