Question

A thermodynamic process is shown in Fig. The pressures and volumes corresponding to some points in the figure are : `P_(A) = 3 xx 10^(4) Pa, P_(B) = 8 xx 10^(4) Pa` and `V_(A) = 2 xx 10^(-3) m^(3) , V_(D) = 5 xx 10^(-3) m`.
In process `AB, 600 J` of heat is added to the system and in process `BC, 200 J` of heat is added to the system. The change in internal energy of the energy of the process `AC` would be.

A. `560 J`
B. `800 J`
C. `600 J`
D. `640 J`

Answer 1

Correct Answer - A
a. By the graph, `W_(AB) = 0` and `W_(BC) = 8 xx 10^(4) [5 - 2] xx 10^(-3) = 240 J`
`:. W_(AC) = W_(AB) + W_(BC) = 0 + 240 = 240 J`
Now, `Delta Q_(AC) = Delta Q_(AB) + Delta Q_(BC) = 600 + 200 = 800 J`
From the first of thermodynamics,
`Delta Q_(AC) = Delta U_(AC) + Delta W_(AC)`
`implies 800 = Delta U_(AC) + 240 implies Delta U_(AC) = 560 J`