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