JEE MAIN - Physics (2020 - 8th January Evening Slot - No. 7)
Consider a mixture of n moles of helium gas
and 2n moles of oxygen gas (molecules taken
to be rigid) as an ideal gas. Its CP/CV value
will be :
23/15
67/45
40/27
19/13
Explanation
$${{{C_P}} \over {{C_V}}} = {{{n_1}{C_{{P_1}}} + {n_2}{C_{{P_2}}}} \over {{n_1}{C_{{V_1}}} + {n_2}{C_{{V_2}}}}}$$
= $${{n \times {{5R} \over 2} + 2n \times {{7R} \over 2}} \over {n \times {{3R} \over 2} + 2n \times {{5R} \over 2}}}$$
= $${{5 + 14} \over {3 + 10}}$$
= $${{19} \over {13}}$$
= $${{n \times {{5R} \over 2} + 2n \times {{7R} \over 2}} \over {n \times {{3R} \over 2} + 2n \times {{5R} \over 2}}}$$
= $${{5 + 14} \over {3 + 10}}$$
= $${{19} \over {13}}$$
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