The work done from A to B can be calculated as, WAB=P×dV =10×(2−1) =10J As the change in volume is zero during the process BC therefore, work done is zero. From first law of thermodynamics, ∆Q=∆U+W The internal energy change in whole process comes out to be 0 . Therefore, Q=W Q=WAB+WBC+WCA Substituting the values in the above equation, we get WCA=5−WAB−WBC =5−10−0=−5J Thus, the magnitude of work in the process A to C is 5 J.