Conversion describes heating that occurs when nonthermal energy is absorbed into tissue and transformed into heat. Which statement is true about conversion?

• A. rate of heat transfer is determined by power of energy source
• B. cooling that occurs when the body is in contact with a cold object
• C. rate of heat transfer is determined by the temperature difference between the thermal agent and the tissue
• D. heat transfer by electromagnetic waves without a medium

Answer: (A)

Conversion heating occurs when nonthermal energy is absorbed by tissue and transformed into heat inside that tissue. The speed at which this heating happens is determined by how much energy is delivered per unit time—the power of the energy source. In other words, higher power means more energy per second is deposited into the tissue, causing a faster rise in temperature (with total heat also depending on exposure time and how well the tissue absorbs that energy). The tissue’s absorption characteristics influence how much energy is taken up, but the rate of heating is set primarily by the source’s power.

The other ideas describe different heat-transfer scenarios. Cooling from contact with a cold object relates to heat loss through conduction driven by temperature differences. The notion that rate is determined by the temperature difference applies more to conduction. Heat transfer by electromagnetic waves without a medium refers to radiation, not conversion heating within tissue.