Q.

The figure shows the P-V plot of an ideal gas taken through a cycle ABCDA. The part ABC is a semi-circle and CDA is half of an ellipse. Then,               [2009]

1 The process during the path AB is isothermal.  
2 Heat flows out of the gas during the path BCD.  
3 Work done during the path ABC is zero.  
4 Positive work is done by the gas in the cycle ABCDA.  

Ans.

(2, 4)

(1)  Process AB is not isothermal. In case of an isothermal process we get a rectangular hyperbola in a P-V diagram.

(2)  In process BCD, ΔU is negative. PV decreases and volume also decreases, therefore W is negative. 

        From first law of thermodynamic, Q is negative i.e., there is a heat loss.

(3)  WAB>WBC. Therefore work done during path ABC is positive.

(4)  Work done in clockwise cycle in a P-V diagram is positive.