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Q.
When an ideal monoatomic gas is heated at constant pressure, the fraction of the heat energy supplied which increases the internal energy of the gas is
By first law of thermodynamics
Q = U + W
$\,\,=\frac{f}{2}nRT+P\int dV=\frac{f}{2}nRT+PV$
or$\quad Q=\frac{f}{2}nRT+nRT\,\,\left(\because \,PV=nRT\right)$
$\quad\quad\quad=\frac{3}{2}nRT+nRT=\frac{5}{2}nRT$
$\therefore \quad$ Fraction of heat energy supplied $=\frac{U}{Q}$
$\quad\quad\quad\quad\quad\quad\quad\quad \quad \quad \quad \quad \quad \quad\,\, =\frac{\left(3/2\right)nRT}{\left(5/2\right)nRT}=\frac{3}{5}\quad$