Q.Draw a p-V diagram and explain the concept of positive and negative work. Give one example each.

Step 1. On a p-V diagram, the area under a curve between an initial and final volume represents the work done, $W = \int p\,dV$ (Section 4.6.3).

Step 2. When a system's volume INCREASES (the curve moves from left to right, toward larger V), the gas is pushing outward against its surroundings — this is positive work done BY the system. Example: gas expanding in a cylinder pushing a piston outward, as in the power (expansion) stroke of a petrol engine.

Step 3. When a system's volume DECREASES (the curve moves from right to left, toward smaller V), the surroundings are pushing inward on the gas — this is negative work done BY the system (equivalently, positive work done ON the system). Example: compressing air inside a bicycle pump by pushing the handle in. …

Use the area-under-the-p-V-curve interpretation of work, and the sign convention that expansion (rising V) is positive work b …

Confusing the sign convention — thinking compression (work done ON the gas) should be called 'positive' just because energy is being put in; by the standard convention used throughout …