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Exam
NEET
Subject
Physics
Chapter
Thermodynamics

NEET · Physics · Thermodynamics

One mole of an ideal monoatomic gas undergoes the process A arrow B...

One mole of an ideal monoatomic gas undergoes the process A→B→C→D→AA \rightarrow B \rightarrow C \rightarrow D \rightarrow A as shown in the graph. The work done during the process is One mole of an ideal monoatomic gas undergoes the process A arrow B arrow C arrow D arrow A as shown in the graph. The

Options

  1. A−52.5×105 J-52.5 \times 10^5 \mathrm{~J}
  2. B−11.5×105 J-11.5 \times 10^5 \mathrm{~J}
  3. C−64×105 J-64 \times 10^5 \mathrm{~J}
  4. D−36×105 J-36 \times 10^5 \mathrm{~J}

Correct answer

A. −52.5×105 J-52.5 \times 10^5 \mathrm{~J}

Step-by-step solution

Process undergone by 1 mole gas is as shown One mole of an ideal monoatomic gas undergoes the process A arrow B arrow C arrow D arrow A as shown in the graph. The
For an ideal monoatomic gas, ratio of specific heat γ=53\gamma=\frac{5}{3} For adiabatic process A→BA \rightarrow B pAVAγ=pBVBγp_A V_A^\gamma=p_B V_B^\gamma Substituting values of pA,pBp_A, p_B and VBV_B from graph, ⇒32×105×VAγ=1×105×(1)γ\Rightarrow \quad 32 \times 10^5 \times V_A^\gamma=1 \times 10^5 \times(1)^\gamma ⇒VAγ=(132)γ\Rightarrow \quad V_A^\gamma=\left(\frac{1}{32}\right)^\gamma Here, γ=53\quad \gamma=\frac{5}{3} ⇒(VA)53=132\Rightarrow \quad\left(V_A\right)^{\frac{5}{3}}=\frac{1}{32} or VA=(132)35=1(25)35=18 m3V_A=\left(\frac{1}{32}\right)^{\frac{3}{5}}=\frac{1}{\left(2^5\right)^{\frac{3}{5}}}=\frac{1}{8} \mathrm{~m}^3 Similarly for adiabatic compression C→DC \rightarrow D, pCVCγ=pDVDγp_C V_C^\gamma=p_D V_D^\gamma We substitute values from graph, ⇒(1×105)×(8)53=(32×105)(VD)53⇒VD5/3=1⇒VD=13/5=1 m3\begin{array}{ll}\Rightarrow & \left(1 \times 10^5\right) \times(8)^{\frac{5}{3}}=\left(32 \times 10^5\right)\left(V_D\right)^{\frac{5}{3}} \\ \Rightarrow & V_D^{5 / 3}=1 \\ \Rightarrow & V_D=1^{3 / 5}=1 \mathrm{~m}^3\end{array} Now, Work done in process A→B→C→D→AA \rightarrow B \rightarrow C \rightarrow D \rightarrow A =WAB+WBC+WCD+WDA=W_{A B}+W_{B C}+W_{C D}+W_{D A} Here we substitute work done for adiabatic process, Wadiabatic =piVi−pfVfγ−1W_{\text{adiabatic }}=\frac{p_i V_i-p_f V_f}{\gamma-1} and work done of isobaric process, Wisobaric =p(Vf−Vi)W_{\text{isobaric }}=p\left(V_f-V_i\right) so, work done in given cycle ABCDAA B C D A =WAB+WBC+WCD+WDA=W_{A B}+W_{B C}+W_{C D}+W_{D A} =(pAVA−pBVB)γ−1+pB(VC−VB)+(pCVC−pDVDγ−1)+pD(VA−VD)\begin{aligned}= & \frac{\left(p_A V_A-p_B V_B\right)}{\gamma-1}+p_B\left(V_C-V_B\right) \\ & \quad+\left(\frac{p_C V_C-p_D V_D}{\gamma-1}\right)+p_D\left(V_A-V_D\right)\end{aligned} Substituting values of pressures and volumes, we get WABCDA=(32×105×18−1×105×153−1)W_{A B C D A}=\left(\frac{32 \times 10^5 \times \frac{1}{8}-1 \times 10^5 \times 1}{\frac{5}{3}-1}\right)+1×105(8−1)+(1×105×8−32×105×153−1)+32×105(18−1)\begin{array}{r}+1 \times 10^5(8-1)+\left(\frac{1 \times 10^5 \times 8-32 \times 10^5 \times 1}{\frac{5}{3}-1}\right) \\ +32 \times 10^5\left(\frac{1}{8}-1\right)\end{array}$\begin{aligned}=\frac{3 \times 10^5 \times 3}{2}+7 \times 10^5 & +\frac{-24 \times 10^5 \times 3}{2} \\ & +4 \times 10^5 \times-7=-52.5 \times 10^5 \mathrm{~J}\end{aligned}
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