Manga , I was wondering about your level, is it Middle school or H.S, well I think the idea can go for both.
Using potato Battery to tell time.
* Two copper electrodes. A 10-cm length of thick (0.64 cm) copper ground wire
works well. You'll find it at hardware and home supply stores.
* Two zinc electrodes. Use large galvanized nails, also available from a
hardware or home supply store.
* Three alligator-clip wires (Radio Shack #278-1156).
* Two potatoes.
Now make a potato clock. Open the battery compartment of the clock and remove
the button battery. In the compartment, notice that there are two connections
for the battery marked plus (+) and minus (-). You'll connect the potato
battery to these two places. Let's call the potatoes A and B. Connect A and B
to the clock like this:
1. Insert a copper electrode and a zinc electrode into each potato, fairly far
2. Use an alligator-clip wire to connect the copper electrode of potato A to
the plus (+) connection in the clock.
3. Use an alligator-clip wire to connect the zinc electrode of potato B to the
negative (-) connection in the clock.
4. Use an alligator-clip wire to connect the zinc electrode of potato A to the
copper electrode of potato B.
I hope that was a help to you.