Understanding Sensible Heat: Definition and Concept

Sensible heat is a type of heat transfer that results in a change in the temperature of a substance without causing a change in its physical state (phase). When you add sensible heat to a liquid or vapor, its temperature goes up. When you remove sensible heat, its temperature goes down. This is different from latent heat, which is absorbed or released during a phase change (like melting, freezing, boiling, or condensation) at a constant temperature.

Analyzing the Options for Sensible Heat

Let's look at the given options in the context of the definition of sensible heat:

• Option 1: "Vaporise water into steam and vice versa". This process involves a change of phase from liquid water to gaseous steam (vaporization) or from steam to water (condensation). The heat involved in phase changes at constant temperature is called latent heat, specifically the latent heat of vaporization. Therefore, this option does not describe sensible heat.
• Option 2: "Change the temperature of a liquid or vapour". This statement perfectly matches the definition of sensible heat. Sensible heat is precisely the heat required to raise or lower the temperature of a substance (like a liquid or vapor) without changing its state. The amount of sensible heat transferred depends on the mass of the substance, its specific heat capacity, and the temperature change.
• Option 3: "Convert water into steam and superheat it". Converting water into steam is a phase change requiring latent heat. Superheating steam involves increasing the temperature of the steam above its boiling point at a given pressure. This latter part (superheating) does involve sensible heat, as it changes the temperature of the vapor. However, the option includes both phase change and temperature change, and sensible heat specifically refers only to the heat causing temperature change without phase change. The primary part mentioned is the phase change. This option is not the most accurate definition of sensible heat alone.
• Option 4: "Measure dew point temperature". The dew point temperature is the temperature at which air becomes saturated with water vapor and condensation begins. Measuring it involves psychrometry and thermodynamics but is not a definition of sensible heat itself. Sensible heat transfer can influence air temperature and thus indirectly affect the dew point condition, but sensible heat is not defined by measuring dew point.

Conclusion on Sensible Heat Definition

Based on the analysis, the definition that accurately describes sensible heat is the heat needed to change the temperature of a substance without changing its state.

Therefore, sensible heat is the heat needed to change the temperature of a liquid or vapour.