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A diatomic ideal gas is used in a Carnot engine as the working substance. If during the adiabatic expansion, part of the cycle and the volume of the gas increases from \(\mathrm{V}\) to \(32 \mathrm{~V}\), the efficiency of the engine is [2010] (A) \(0.25\) (B) \(0.5\) (C) \(0.75\) (D) \(0.99\)

Short Answer

Expert verified
The efficiency of the Carnot engine during the adiabatic expansion when the volume of the gas increases from V to 32V is approximately \(0.5\) or \(50\%\). This is calculated using the formulas for adiabatic expansion and the properties of a diatomic ideal gas to find the temperatures of the hot and cold reservoirs, and then using the efficiency formula for Carnot engine. Therefore, the correct answer is (B) 0.5.

Step by step solution

01

For a diatomic ideal gas, the adiabatic expansion process can be described using the formula: \(P_1V_1^{\gamma} = P_2V_2^{\gamma}\) where \(P_1\) and \(P_2\) are the initial and final pressures, \(V_1\) and \(V_2\) are the initial and final volumes, and \(\gamma\) is the heat capacity ratio (\(\gamma = \frac{C_P}{C_V} = \frac{7}{5} \) for a diatomic ideal gas). We are given that \(V_2 = 32V_1\), so the formula becomes: \(P_1V_1^{\frac{7}{5}} = P_2(32V_1)^{\frac{7}{5}}\) #Step 2: Relate the temperatures and pressures#

We can relate the temperatures and pressures of the gas using the ideal gas law: \(P_1V_1 = nR T_1\) \(P_2V_2 = nR T_2\) where \(n\) is the number of moles of gas, \(R\) is the gas constant, and \(T_1\) and \(T_2\) are the temperatures before and after expansion, respectively. Dividing the second equation by the first equation, we get: \(\frac{P_2}{P_1} = \frac{T_2}{T_1}\frac{V_2}{V_1}\) Substitute \(V_2 = 32V_1\): \(\frac{P_2}{P_1} = 32\frac{T_2}{T_1}\) #Step 3: Solve for the temperature ratio#
02

Now, we substitute the expression for \(\frac{P_2}{P_1}\) from Step 1 into Step 2, and solve for the temperature ratio: \(32\frac{T_2}{T_1} = \left(\frac{V_1}{32V_1}\right)^{\frac{7}{5}}\) \(\frac{T_2}{T_1} = \frac{1}{32^{\frac{2}{5}}}\) #Step 4: Calculate the efficiency#

Using the efficiency formula for Carnot engine, we substitute the temperature ratio and find the efficiency: Efficiency = \(1 - \frac{T_2}{T_1} = 1 - \frac{1}{32^{\frac{2}{5}}}\) Efficiency ≈ 0.5 So, the efficiency of the engine is about 0.5 or 50%. Therefore, the correct answer is (B) 0.5.

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