Discussion of the experimental?
Why was my expectations wrong?
The answer was that we didn't know the principle of fruit battery.
Processes of electricity generation are these.
1.Metal is melted by the liquid.(※Acid melted metals.)
2.Electricity was generated by melting metal, it flows from aluminium to the copper.
3.Miniature bulb shines by the electricity flowing.
Perhaps, the caused which our expectations is wrong is that we have already determined that the liquid is not melted metal.
In case that metals are not melted, electricity is not generated.
There is also a possibility that "Though metals are dissolved a little weak, was too weak to shine a battery."