2. Questions Bank
  3. JEE Main & Advanced
  4. Physics
  5. Thermodynamical Processes

JEE Main & Advanced Physics Thermodynamical Processes Question Bank First Law of Thermodynamics

  • question_answer
    The specific heat of hydrogen gas at constant pressure is \[{{C}_{P}}=3.4\times {{10}^{3}}cal/kg{{\,}^{o}}C\] and at constant volume is \[{{C}_{V}}=2.4\times {{10}^{3}}cal/kg{{\,}^{o}}C.\]If one kilogram hydrogen gas is heated from \[{{10}^{o}}C\] to \[{{20}^{o}}C\] at constant pressure, the external work done on the gas to maintain it at constant pressure is                                               [MP PMT 1995; DPMT 2001]

    A)            \[{{10}^{5}}\,\]cal              

    B)            \[{{10}^{4}}\]cal

    C)            \[{{10}^{3}}\] cal                

    D)            \[5\times {{10}^{3}}\]cal

    Correct Answer: B

    Solution :

                        From FLOT DQ = DU + DW Work done at constant pressure \[{{(\Delta W)}_{P}}={{(\Delta Q)}_{P}}-\Delta U\] \[{{(\Delta Q)}_{P}}-{{(\Delta Q)}_{V}}\] (As we know \[{{(\Delta Q)}_{V}}=\Delta U\]) Also \[{{(\Delta Q)}_{P}}=m{{c}_{P}}\Delta T\] and \[{{(\Delta Q)}_{V}}=m{{c}_{V}}\Delta T\] Þ \[{{(\Delta W)}_{P}}=m({{c}_{P}}-{{c}_{V}})\Delta T\]            Þ \[{{(\Delta W)}_{P}}=1\times (3.4\times {{10}^{3}}-2.4\times {{10}^{3}})\times 10={{10}^{4}}cal\]


You need to login to perform this action.
You will be redirected in 3 sec spinner