Question 11 MODE01 - Chief MODU Engineer

The Correct Answer is A. **Why option A ("pressure/volume") is correct:** The indicator card diagram is, by definition, a plot of pressure (P) against volume (V) for the working fluid inside an engine cylinder (such as a reciprocating internal combustion engine or steam engine) over one complete cycle. In thermodynamics, the area enclosed by a cycle on a pressure-volume (P-V) diagram represents the net work done by the system on its surroundings during that cycle ($\text{Work} = \oint P dV$). Therefore, when analyzing the indicator card diagram and calculating the area within the curve, you are directly calculating the work output (indicated work) from the cylinder. **Why each of the other options is incorrect:** * **B) temperature/entropy (T-S diagram):** A T-S diagram is used to analyze thermodynamic cycles, but the area under the curve represents heat transfer, not mechanical work output. While related to engine efficiency, it is not the diagram used for calculating work via area in an indicator card analysis. * **C) pressure/enthalpy (P-H diagram):** P-H diagrams are primarily used in refrigeration and air conditioning cycles (vapor compression cycles) to track properties like enthalpy. The area on this diagram does not represent the net work output of the engine cycle. * **D) pressure/temperature (P-T diagram):** A P-T diagram (or phase diagram) shows the relationship between pressure and temperature for different phases (solid, liquid, gas) of a substance. It is not used to calculate mechanical work output by finding the area within a cyclic curve.