All power supplies are connected in a simple electrical console which incorporates the necessary electrical connections for the air pump and the sensors. The pressure P, vacuum V and temperatures T1 & T2 measured inside the two vessels are displayed on a common digital meter with a rotator selector switch. IFD5 An I/O Data Port connector on the right hand side of the console allows the voltage signals from each of the measurements to be connected to a suitable PC using an Armfield interface device (IFD5). The IFD5 connects to the electrical console via a 50-way data cable, and to the PC by means of the USB cable. The 50-way IDC header carries signals to and from the equipment. A red LED lights when the unit is connected to the PC, and a green LED lights ‘Power’ ‘Active’ when the unit has been recognized by the PC. Determination of Heat Capacity For a perfect gas, Cp = Cv + R Where Cp = molar heat capacity at constant pressure Cv = heat capacity at constant volume The heat capacity can be determined experimentally using a two-step process: An adiabatic reversible expansion from the initial pressure Ps to an intermediate pressure Pi. {Ps, Vs, Ts} {Pi, Vi, Ti} A return of the temperature to its original value Ts at constant volume. {Pi, Vi, Ti} {Pf, Vi, Ts} For a reversible adiabatic expansion, dq = 0 From the first law of thermodynamics, dU = dq + dW Therefore during the expansion process, dU = dW = -pdV At constant volume, the heat capacity relates the change in temperature to change in internal energy: dU = CvdT Thus, CvdT = -pdV Substituting in the gas equation and then integrating gives: Cv ln = -R ln
All power supplies are connected in a simple electrical console which incorporates the necessary electrical connections for the air pump and the sensors. The pressure P, vacuum V and temperatures T1 & T2 measured inside the two vessels are displayed on a common digital meter with a rotator selector switch. IFD5 An I/O Data Port connector on the right hand side of the console allows the voltage signals from each of the measurements to be connected to a suitable PC using an Armfield interface device (IFD5). The IFD5 connects to the electrical console via a 50-way data cable, and to the PC by means of the USB cable. The 50-way IDC header carries signals to and from the equipment. A red ‘Power’ LED lights when the unit is connected to the PC, and a green ‘Active’ LED lights when the unit has been recognized by the PC. Determination of Heat Capacity For a perfect gas, Cp = Cv + R Where Cp = molar heat capacity at constant pressure Cv = heat capacity at constant volume The heat capacity can be determined experimentally using a two-step process: An adiabatic reversible expansion from the initial pressure Ps to an intermediate pressure Pi. {Ps, Vs, Ts} {Pi, Vi, Ti} A return of the temperature to its original value Ts at constant volume. {Pi, Vi, Ti} {Pf, Vi, Ts} For a reversible adiabatic expansion, dq = 0 From the first law of thermodynamics, dU = dq + dW Therefore during the expansion process, dU = dW = -pdV At constant volume, the heat capacity relates the change in temperature to change in internal energy: dU = CvdT Thus, CvdT = -pdV Substituting in the gas equation and then integrating gives: Cv ln = -R ln