According to Boyle's law, isothermal compression has:
(p0-h)SL 1=p0SL2
L2 = 30cm
After rebalancing, the mercury levels on both sides are equal, and the gas length is shortened by 10cm, so it is necessary to inject10+19+10 = 39cm of mercury.
(2) the gas is compressed, which is the positive work done by the outside world on the gas;
When the temperature of gas is constant, so is the internal energy. According to the formula of the first law of thermodynamics △U=W+Q, gas gives off heat.
Answer: ① another 39cm mercury column needs to be injected; At this time, the length of the gas column at the closed end is 30cm；;
② In the process of injecting mercury, the outside world does positive work on the enclosed air, and the gas will release heat.