JEE Advanced2018PhysicsThermodynamicsActual
One mole of an ideal monatomic gas undergoes an adiabatic expansion in which its volume becomes eight times its initial value. If the initial temperature of the gas is 100   K and the universal gas constant R = 8.0  J   mo l - 1  K - 1 , then how much is the decrease in its internal energy (in J ) ?
Correct answer
900
Step-by-step solution
V i = V V f = 8 V For adiabatic process γ = 5/ 3 for monoatomic gas T 1 ⋅ V 1 γ − 1 = T 2 ⋅ V 2 γ − 1 100 V 2 3 = T 2 8 V 2 3 T 2 = 25   K Loss in internal energy ∆ U = n C v ∆ T = 1 f R 2 100 - 25 = 12 × 75 = 900   J