题目

The English writer Samuel Johnson famously said, “You find no man who is willing to leave London. No, sir, when a man is tired of London, he is tired of life, for there is in London all that life can afford.” More than two centuries have passed since Johnson’s age, but his words still ring true. Here, you’ll find the historic Tower of London and the Tate Modern both considered must-sees. Shakespeare’s sonnets（十四行诗） are still being uttered by actors. Londoners most certainly still look up to the royals, but they also rock out to Coldplay and Lily Allen. And while th19．如图所示的电路中，电阻R2的电阻为10欧，断开电键S，电流表的示数为0.4安，闭合电键S，电流表的示数为1.2安．求：（1）电源电压；（2）R1的阻值．