- The U-tube in figure 2-18, of uniform cross section 1 cm^2, contains mercury to the depth shown. The barometric pressure is 750 Torr. The left side of the tube is now closed at the top and the right side is connected to a good vacuum pump. A) How far does the mercury level fall in the left side and b) what is the final pressure of the trapped air? The temperature remains constant.
- Pv = RT
Hi, just reviewing some thermodynamics from the textbook by Sears and Salinger, having a hard time conceptualizing this one. It's an isothermal change in pressure, so the volumes of the mercury and the air both change to reach equilibrium, but if it's a "good vacuum pump", then won't the right side be completely evacuated, and the mercury sucked completely into the right side? Half of the air molecules will be evacuated, so all else being equal, the pressure of the air should be reduced by half, but because of this arrangement, we have one end of the mercury subject to zero pressure and the other subject to normal pressure. I just don't see how any end state can be specified besides all of the mercury sucked into the right side of the tube. Thanks in advance for any hints!