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(B) For a process at constant pressure,the first law of thermodynamics is given by $Q = \Delta U + W$.The heat supplied is $Q = n C_p \Delta T$.The ch

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$40$

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(B) For a process at constant pressure,the first law of thermodynamics is given by $Q = \Delta U + W$.The heat supplied is $Q = n C_p \Delta T$.The change in internal energy is $\Delta U = n C_v \Delta T$.The external work done is $W = Q - \Delta U = n C_p \Delta T - n C_v \Delta T = n (C_p - C_v) \Delta T = n R \Delta T$.For a monoatomic gas,$C_v = \frac{3}{2} R$ and $C_p = \frac{5}{2} R$.The fraction of heat used for work is $\frac{W}{Q} = \frac{n R \Delta T}{n C_p \Delta T} = \frac{R}{C_p} = \frac{R}{\frac{5}{2} R} = \frac{2}{5}$.Converting to percentage: $\frac{2}{5} 	imes 100 \% = 40 \%$.

$A$ monoatomic gas is heated at constant pressure. The percentage of total heat used for doing external work is (in $\%$)

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