Lemons are acidic, which means they have H+ ions in them. H+ ions conduct electricity well (positively charged particles). If lemon juice is put in one container with a bar of Zn (zinc) which is connected to a metal wire (which you will then connect to the clock), then get another container with a bar of Cu (copper) in it which is connected to another metal wire (which you will connect to the other side of the clock) and fill that container with a base (bases have OH- ions in them) (negatively charged particles), then also put a "salt bridge"(can be a glass tube with 2 right angles(looks like the letter "n") filled with salt water without any air bubbles in it(you should put a salt "cork" in both ends of the tube to seal it so no salt water gets out)) between the containers (purpose of the