The difference in temperature between the cold source and tissue surface describes which concept?

• A. Energy transfer
• B. Thermal capacity
• C. Phase change
• D. Radiation

Answer: (A)

The key idea here is energy transfer driven by a temperature gradient. When there’s a difference between the cold source and the tissue surface, heat will move from the warmer region to the cooler one. That temperature difference acts as the driving force for heat flow, and the rate of transfer grows as the gradient increases. In practical terms, this transfer happens mainly through conduction when the two objects are in contact, though convection or radiation can also play a role depending on the situation. Thermal capacity is about how much energy is needed to change temperature, not the driving force for transfer. Phase change involves latent energy during state changes and isn’t about the ongoing gradient. Radiation is one way heat can move, but describing the situation as energy transfer emphasizes the overall process caused by the temperature difference.