An ideal gas of mass m in a state A goes to another state. B via three different processes as shown in the given figure. If Q₁, Q₂ and Q₃ denote the heat absorbed by the gas along the three paths, then :

Q₁ > Q₂ > Q₃

Change in internal energy is path independent and depends only on the initial and final states As the initial and final states in the three processes are same. Therefore

$ \Delta u_1 = \Delta u_2 = \Delta u_3$

$\text{ Work done W = area under P-V diagram}$

$\text{ Area under curve 1 > Area under curve 2 > Area under curve 3} \Rightarrow W_1 > W_2>W_3$

$\text{According to first law of thermodynamics } Q = \Delta u + W$ 

Since $ W_1 > W_2 >W_3 , \Delta u_1 = \Delta u_2 = \Delta u_3$  

$\Rightarrow Q_1 > Q_2> Q_3$