Option 1 states that any energy transfer that does not involve a temperature difference is not heat. This means that heat transfer occurs only when there is a difference in temperature between two objects. Heat transfer is the transfer of thermal energy from an object at a higher temperature to an object at a lower temperature. Therefore, if there is no temperature difference, there will be no heat transfer.
Option 2 states that any energy transfer always requires a temperature difference. This is incorrect because there are forms of energy transfer, such as mechanical work or electromagnetic radiation, that do not rely on a temperature difference.
Option 3 states that on heating, the length and volume of an object remain exactly the same. This statement is unrelated to the concept of heat transfer and is incorrect. Heating can cause expansion, resulting in changes in length and volume of an object.
Option 4 states that whenever there is a temperature difference, heat is the only way of energy transfer. This is incorrect because there are other forms of energy transfer, such as conduction, convection, and radiation, that can occur in addition to heat transfer.
Therefore, option 1 is the correct statement as it accurately represents the relationship between energy transfer, temperature difference, and heat.