Electricity and Judaism

I wish to know more about why I cannot switch on and listen to the radio on shabbos, or use a condensor to turn on a florescent light bulb. On the other hand, it appears that I am permitted to use an elevator, but not to touch the sensor that summons it. This makes no sense to me. If you can recommend a good book - in English (my Spanish is rusty) that explains this, please let me know. Otherwise, I feel the pull of a thread that could well unravel the entire moral edifice I have adopted for myself. (Darn you apostate Jew Richard Feynman!)