The first law of thermodynamics can be written as $\Delta U = (+q) + (+w)$, where $\Delta U$ is the increase in internal energy of the system. State the meaning of $+q$ and $+w$.
Figure 2.1 shows how the volume $V$ of a fixed mass of ideal gas varies with pressure $p$. The gas completes a cycle of changes $A$ to $B$ to $C$ to $A$. In the change from $A$ to $B$, the gas volume increases from $2.3 \times 10^{-3}\,\text{m}^3$ to $3.8 \times 10^{-3}\,\text{m}^3$.
Show that the size of the work done during the change $A$ to $B$ is $390\,\text{J}$.
State and explain the total change, if any, in the internal energy of the gas during one complete cycle.
For the change $A$ to $B$, $1370\,\text{J}$ of thermal energy is transferred to the gas. For the change $B$ to $C$, no thermal energy enters or leaves the gas. The work done on the gas during this change is $550\,\text{J}$. Use these details together with the information in (b) to complete Table 2.1.
Show that the magnitude of the work done during the change A to B is $390\,\text{J}$.
State and explain the total change, if any, in the internal energy of the gas during one complete cycle.