Question

A gas can be taken from A to B via two different processes ACB and ADB.

When path ACB is used 60 J of heat flows into the system and 30 J of work is done by the system. If path ADB is used work done by the system is 10 J. The heat Flow into the system in path ADB is : 

(1) 80 J

(2) 20 J

(3) 100 J

(4) 40 J

Answer 1

Ans: (4) 40 J

Sol:

∆Q_ACB = ∆W_ACB + ∆U_ACB

⇒ 60 J = 30 J + ∆U_ACB

⇒ ∆U_ACB = 30 J 

⇒ ∆U_ADB = ∆U_ACB = 30 J 

∆Q_ACD = ∆U_ACB + ∆W_ADB

= 10 J + 30 J = 40 J